EP2228527A2

EP2228527A2 - Controller for internal combustion engine

Info

Publication number: EP2228527A2
Application number: EP10156211A
Authority: EP
Inventors: Yoshifumi Nakamura; Masatomi Yoshihara; Akito Uchida; Kouji Okamura; Yuuji Hatta; Misao Shibata
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2009-03-12
Filing date: 2010-03-11
Publication date: 2010-09-15
Also published as: EP2228527A3; JP2010209891A

Abstract

When the internal combustion engine (11) is stopped, the ECU (41) controls the load torque of the alternator (34) so that the engine rotational speed (NE) coincides with the target engine rotational speed. By so doing, the ECU (41) executes stop position control in which the internal combustion engine (11) is stopped so that the crank angle θ at the time of engine stop stops within the target crank angle range. While the stop position control is being executed, the ECU (41) calculates a required load torque necessary to make the engine rotational speed (NE) coincide with the target engine rotational speed (NEtg), and then compares the required load torque with the maximum load torque of the alternator (34) at the engine rotational speed (NE) at that time. Then, when the required load torque is larger than the maximum load torque, the ECU (41) ends the stop position control.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a controller for an internal combustion engine, which controls a crank angle at the time when the internal combustion engine stops.

2. Description of the Related Art

In recent years, in order to improve fuel economy and reduce exhaust gas, a controller for an internal combustion engine, which causes the internal combustion engine to automatically stop when a vehicle stops and which causes the internal combustion engine to automatically restart when the vehicle is operated to drive off, has been practically used (for example, Japanese Patent Application Publication No. 2006-170068 ( JP-A-2006-170068 )). In addition, there is suggested such a controller for an internal combustion engine, which executes stop position control in which, when the internal combustion engine is stopped, a crank angle at the time of engine stop is made to fall within an angular range suitable for a restart in order to reduce starting time at the time of engine restart.
For example, a controller for an internal combustion engine as described in Japanese Patent Application Publication No. 2008-215230 ( JP-A-2008-215230 ), calculates the behavior of an engine rotational speed (target rotational behavior) until the engine rotation stops at a target crank angle, and a load torque of an auxiliary equipment is controlled so that an actual rotational behavior coincides with the target rotational behavior. By so doing, the internal combustion engine stops at the crank angle that falls within a target crank angle range. Specifically, the target rotational behavior is expressed by the relationship between a crank angle and a target engine rotational speed, and the target engine rotational speed is obtained by calculating a crank angle back from a target crank angle on the basis of law of conservation of energy in consideration of a friction loss of the engine, or the like. Then, in the thus configured internal combustion engine, as a predetermined stop condition is satisfied, a load torque of an alternator is controlled so that an actual engine rotational speed becomes a target engine rotational speed corresponding to the crank angle at that time, thus controlling the crank angle at the time of engine stop.
Incidentally, the engine rotational speed at the beginning of stop position control varies depending on, for example, a difference in engine rotational speed during idling, or the like. Therefore, at the beginning of stop position control, an actual engine rotational speed may exceed a target engine rotational speed to cause a large gap between the actual engine rotational speed and the target engine rotational speed. In addition, because of, for example, spontaneous fluctuations in friction loss, or the like, a variation with respect to the crank angle of an actual engine rotational speed may differ from a variation in a calculated target engine rotational speed. Thus, the actual engine rotational speed may exceed the target engine rotational speed to cause a large gap between the actual engine rotational speed and the target engine rotational speed. Then, when an actual engine rotational speed exceeds a target engine rotational speed because of the above described various reasons to cause a large gap between the actual engine rotational speed and the target engine rotational speed, a required load torque necessary to make an actual engine rotational speed coincide with a target engine rotational speed may exceed a maximum load torque of an alternator at that engine rotational speed.
In such a case, even when a load torque of the alternator is controlled as described in JP-A-2008-215230 , it is difficult to stop the internal combustion engine at the crank angle that falls within the target crank angle range. Furthermore, the alternator is driven to generate electric power, so the alternator may be unnecessarily operated to, for example, overcharge a battery.
Note that the above problems are not limited to when a load torque of the alternator is controlled; the above problems also occur even when a load torque of another auxiliary equipment is controlled.

SUMMARY OF THE INVENTION

The invention provides a controller for an internal combustion engine, which is able to prevent unnecessary operation of an auxiliary equipment when a crank angle is controlled at the time when the internal combustion engine stops.
A first aspect of the invention relates to a controller for an internal combustion engine. The controller includes: target rotational behavior calculation means that calculates a target rotational behavior of the internal combustion engine until the internal combustion engine stops at a crank angle that is equal to a target crank angle; and stop position control means that executes stop position control in which, when the internal combustion engine is stopped, a load torque of an auxiliary equipment of the internal combustion engine is controlled so that an actual rotational behavior of the internal combustion engine coincides with the target rotational behavior, and the internal combustion engine is stopped so that the crank angle falls within a target crank angle range. The stop position control means includes comparing means that compares a required load torque, necessary to make the actual rotational behavior of the internal combustion engine coincide with the target rotational behavior, with a maximum load torque of the auxiliary equipment at an operating state of the internal combustion engine at that time, and, the stop position control means ends the stop position control when the comparing means determines that the required load torque is larger than the maximum load torque of the auxiliary equipment.
With the above configuration, when the crank angle at the time when the internal combustion engine stops is controlled by executing stop position control, the stop position control is ended when the required load torque is larger than the maximum load torque of the auxiliary equipment in the operating state of the internal combustion engine at that time, that is, when it is impossible to stop the engine at the crank angle that falls within the target crank angle range even when the load torque of the auxiliary equipment is controlled. Thus, it is possible to prevent unnecessary operation of the auxiliary equipment.
In the controller for an internal combustion engine, the auxiliary equipment may be an alternator that is driven by the internal combustion engine to generate electric power. In addition, the auxiliary equipment may be a compressor of a vehicle air conditioner.
In addition, the controller for an internal combustion engine may further include automatic stop-restart control means that automatically stops the internal combustion engine when a predetermined stop condition is satisfied and that automatically restarts the internal combustion engine when a predetermined restart condition is satisfied.
With the above configuration, when a predetermined stop condition is satisfied, such as when the vehicle is stopped, control for automatically stopping the internal combustion engine, so-called idling stop, is executed. Thus, the stop position control is frequently executed. Thus, there is an increase in chance of unnecessary operation of the auxiliary equipment during stop position control, so it is desirable to appropriately prevent unnecessary operation of the auxiliary equipment. In terms of this point, by applying the controller for an internal combustion engine to the above configuration, it is possible to prevent unnecessary operation of the auxiliary equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic view that shows an internal combustion engine, to which a controller for an internal combustion engine according to an embodiment of the invention is applied, and its peripheral configuration;
FIG. 2 is a view that illustrates a table of a target rotational behavior;
FIG. 3 is a graph that illustrates a method of calculating a target rotational behavior;
FIG. 4 is a schematic view that shows a map for calculating a torque loss;
FIG. 5 is a graph that shows the relationship between an engine rotational speed and a load torque of an alternator;
FIG. 6 is a map that schematically shows required load torque characteristics;
FIG. 7 is a flowchart that shows the control procedure of stop position control, executed by the controller for an internal combustion engine according to the embodiment;
FIG. 8 is a flowchart that shows the control procedure of calculating a target rotational behavior, executed by the controller for an internal combustion engine according to the embodiment; and
FIG. 9 is a flowchart that shows the control procedure of calculating a required load torque, executed by the controller for an internal combustion engine according to the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a specific embodiment of a controller for an internal combustion engine according to the invention will be described with reference to the accompanying drawings. An internal combustion engine 11 according to the present embodiment is a multi-cylinder internal combustion engine having a plurality of cylinders 12. FIG. 1 schematically shows one of the plurality of cylinders 12. As shown in the drawing, a piston 13 is accommodated in each cylinder 12 of the internal combustion engine 11 so as to allow a reciprocating movement. By so doing, a combustion chamber 14 is defined in each cylinder 12 by the top surface of the piston 13 and the inner peripheral surface of the cylinder 12. In addition, an intake passage 15 and an exhaust passage 16 are connected to an upper side of each combustion chamber 14 and can be brought into communication with each combustion chamber 14. Furthermore, an intake valve 17 and an exhaust valve 18 are provided at the upper side of each combustion chamber 14. Each intake valve 17 allows or shuts off fluid communication between the intake passage 15 and a corresponding one of the combustion chambers 14. Each exhaust valve 18 allows or shuts off fluid communication between the exhaust passage 16 and a corresponding one of the combustion chambers 14.
A fuel injection valve 21 is provided in an intake port of each cylinder downstream of the intake passage 15. The fuel injection valve 21 injects fuel toward a corresponding one of the combustion chambers 14. In addition, an ignition plug 22 is provided at the upper side of each combustion chamber 14. The ignition plug 22 is used to spark ignite a mixture of injected fuel and intake air inside a corresponding one of the combustion chambers 14.
In addition, a crankshaft 31 is rotated as the pistons 13 perform a reciprocating movement, and a crank pulley 32 is coupled to the crankshaft 31. An alternator 34, which serves as an auxiliary equipment, is drivably coupled to the crank pulley 32 via a belt 33. The belt 33 transmits the rotation of the crank pulley 32. By so doing, the alternator 34 is driven for rotation by the driving force of the internal combustion engine 11 to generate electric power. Then, by carrying out duty control on electric current (field current) generated by the alternator 34, it is possible to control a load applied to the internal combustion engine 11 by the alternator 34. Note that a battery 35 that supplies electric power to various electrical devices (not shown), or the like, is electrically connected to the alternator 34, and the battery 35 is charged with electric power generated by the alternator 34.
In the above configuration, as the intake valve 17 opens, fuel injected from the fuel injection valve 21 and intake air become an air-fuel mixture, and the air-fuel mixture is supplied into a corresponding one of the combustion chambers 14. After that, the air-fuel mixture is ignited by the ignition plug 22, so the air-fuel mixture combusts to push down the piston 13 by the combustion pressure. High-temperature and high-pressure combustion gas generated at this time causes the piston 13 to reciprocally move. Thus, the crankshaft 31 is rotated, so that the driving force of the internal combustion engine 11 is obtained, and auxiliary equipments, such as the alternator 34, are driven. Note that, as the exhaust valve 18 opens, the air-fuel mixture that has combusted is exhausted to the exhaust passage 16 as exhaust gas.
These various controls for the internal combustion engine 11 are executed by an electronic control unit (hereinafter, referred to as ECU) 41 mounted on a vehicle. The ECU 41 serves as target rotational behavior calculation means, stop position control means, comparing means and automatic stop-restart control means. The ECU 41 includes a CPU, a ROM, a RAM, an input port, an output port, and the like. The CPU executes processing related to control over the internal combustion engine 11. The ROM stores programs and data necessary for that control. The RAM temporarily stores the processing results of the CPU. The input port is used to input signals from external devices. The output port is used to output signals to external devices.
Various sensors are connected to the input port of the ECU 41. The various sensors detect the state of the internal combustion engine 11 and the state of the vehicle. The various sensors include a crank position sensor 42, an accelerator position sensor 43, a brake sensor 44, a coolant temperature sensor 45, a vehicle speed sensor 46, and the like. The crank position sensor 42 detects a crank angle θ, which is a rotation angle of the crankshaft 31, and an engine rotational speed NE, which is a rotational speed. The accelerator position sensor 43 detects an accelerator operation amount. The brake sensor 44 detects a state in which a brake pedal is operated. The coolant temperature sensor 45 detects a temperature of coolant for the internal combustion engine 11. The vehicle speed sensor 46 detects a vehicle traveling speed. On the other hand, the fuel injection valves 21, the alternator 34, and the like, are electrically connected to the output port of the ECU 41. Then, the ECU 41 executes various controls over a fuel injection amount, a power generation amount, and the like, on the basis of the results detected by these various sensors.
In addition, the ECU 41 executes automatic stop-restart control in which the internal combustion engine 11 is automatically stopped when a predetermined stop condition is satisfied, and the internal combustion engine 11 is automatically restarted when a predetermined restart condition is satisfied.
In the automatic stop-restart control, when a predetermined stop condition is satisfied, for example, when if it is determined that a predetermined period of time Δt has elapsed in a state where the brake pedal is depressed and the vehicle is stopped, the ECU 41 stops fuel injection to automatically stop the internal combustion engine 11. In addition, when the internal combustion engine 11 is automatically stopped, and when a predetermined restart condition, for example, depression of the brake pedal is released, is satisfied, the ECU 41 determines that an engine start instruction is output to the internal combustion engine 11 to drive a starter motor (not shown) to thereby automatically restart the internal combustion engine 11. Note that the ECU 41 executes the above automatic stop-restart control on the basis of the results detected by the above described crank position sensor 42, accelerator position sensor 43, brake sensor 44, coolant temperature sensor 45, vehicle speed sensor 46, and the like, and the amount of charge of the battery 35, or the like. In addition, the stop condition and the restart condition for the internal combustion engine 11 are not limited to the above conditions. For example, in addition to the above conditions, the stop condition and the restart condition may be set on the basis of a gear shift position, or the like.
In addition, when the predetermined stop condition is satisfied and an engine stop request is issued, the ECU 41 according to the present embodiment executes stop position control in which the internal combustion engine 11 is stopped so that the engine stops at the crank angle θ that falls within a target crank angle range. In the stop position control, the ECU 41 calculates the behavior of the engine rotational speed (target rotational behavior) until the engine rotation stops at the target crank angle, and controls a load torque of the alternator 34 so that the actual rotational behavior coincides with the target rotational behavior.
More specifically, the target rotational behavior is expressed by the relationship between the crank angle θ and the target engine rotational speed NEtg until the internal combustion engine 11 stops at the target crank angle, and, as shown in FIG. 2, the target rotational behavior is expressed by allocating the target engine rotational speed NEtg calculated at each predetermined crank angle interval to a table. Note that, in FIG. 2, the crank angle θ is expressed by a crank angle (ATDC) with reference to an intake top dead center of the cylinder 12, the target crank angle is 60CA, and a target engine rotational speed NEtg calculated at each 30CA from that angle is shown. In addition, "n" in FIG. 2 indicates the number of times the crank angle θ attains a top dead center (TDC) until the engine stops.
The target engine rotational speed NEtg is calculated using the following mathematical expression (1) based on law of conservation of energy in consideration of a friction loss of the engine, or the like, back from the target crank angle as an initial value as shown in FIG. 3.
$NEtg {(i + 1)}^{2} = NEtg {(i)}^{2} - \frac{2}{J} \{T loss (θ (i)) - Tref (NEtg (i))\}$
Here, "i" in FIG. 2 and the above mathematical expression (1) is a numerical value that indicates the number of calculations starting from the target engine rotational speed NEtg(0) at the target crank angle. That is, "NEtg(i+1)" indicates a target engine rotational speed NEtg the predetermined crank angle before "NEtg(i)". In addition, "J" is the moment of inertia of the internal combustion engine 11, and "Tloss(θ(i)))" is a torque loss resulting from the total of a pumping loss and a friction loss at a current crank angle θ(i). The torque loss Tloss(θ(i)) is calculated on the basis of the crank angle θ(i) using a predetermined map shown in FIG. 4. In addition, "Tref(NEtg(i))" is a reference load torque of the alternator 34 at a current target engine rotational speed NEtg(i). The reference load torque Tref(NEtg(i)) is calculated on the basis of the target engine rotational speed NEtg(i) using a predetermined map shown in FIG. 5.
In the present embodiment, the reference load torque Tref(NEtg(i)) is set at half the maximum load of the alternator 34 at the target engine rotational speed NEtg(i) at that time. By so doing, even an alternator 34 that is not able to output assist torque is able to virtually control the load torque of the alternator 34 in both positive and negative directions. That is, it is possible to control the load torque of the alternator 34 in such a manner that a load torque smaller than a reference load Tref is virtually regarded as a negative load torque (assist torque) and a load torque larger than the reference load Tref is virtually regarded as a positive load torque. By so doing, the trackability of an actual engine rotational speed NE to a target engine rotational speed NEtg may be improved.
Note that the reference load torque Tref(NEtg(i)) of the alternator 34 is not limited to half the maximum load; instead, any load may be set as a reference load torque Tref(NEtg(i)) as long as the load is smaller than a maximum load torque Tmax that can be controlled by the alternator 34 and is larger than 0.
Then, until the target engine rotational speed NEtg(i+1) exceeds a maximum engine rotational speed NEmax at or below which stop position control is executable, the ECU 41 repeats calculation of the above mathematical expression (1) and then completes calculation of the target rotational behavior.
Subsequently, the ECU 41 detects the engine rotational speed NE at each crank angle θ ( ATDC 0, 30, 60, 90, 120, 150CA) at which the target engine rotational speed NEtg is calculated, and determines a value of the number of calculations i at which the crank angle θ and the target engine rotational speed NEtg are closest to the above crank angle θ and the engine rotational speed NE by referring to the table shown in FIG. 2. Then, a required load torque Td, which is a load torque necessary to make the engine rotational speed NE coincide with the target engine rotational speed NEtg at that number of calculations i, is calculated on the basis of the following mathematical expression (2).
$Td (i) = \frac{J \cdot K}{2 \cdot Δ θ} ({Ne}^{2} - Netg {(i)}^{2}) + Tref (Ne)$
Here, "J" is a moment of inertia of the internal combustion engine 11, "K" is a feedback gain, and "Δθ" is an amount of change in crank angle (30CA in the present embodiment).
Then, the ECU 41 multiplies the required load torque Td by a pulley ratio to convert the required load torque Td into a required shaft torque Tdf of the alternator 34, and then detects the voltage of the battery 35. Subsequently, the ECU 41 selects a required load torque characteristic map corresponding to the current battery voltage from among a plurality of required load torque characteristic maps generated respectively for battery voltages as shown in FIG. 6, and calculates a power generation instruction (Duty) corresponding to the current required shaft torque Tdf and engine rotational speed NE. Then, the ECU 41 controls the power generation control current of the alternator 34 on the basis of the power generation instruction to control the load torque of the alternator 34. By so doing, the engine rotational speed NE coincides with the target engine rotational speed NEtg, and it is possible to stop the engine so that the crank angle θ falls within the target crank angle range.
Incidentally, the engine rotational speed NE may exceed the target engine rotational speed NEtg because of, for example, a difference in engine rotational speed during idling, spontaneous fluctuations in friction loss, or the like. Then, when a large gap occurs between the engine rotational speed NE and the target engine rotational speed NEtg, a required load torque Td necessary to make the engine rotational speed NE coincide with the target engine rotational speed NEtg may exceed a maximum load torque of the alternator 34 at the engine rotational speed NE at that time. In such a case, even when the load torque of the alternator 34 is controlled, not only it is impossible to stop the internal combustion engine at the crank angle θ that falls within the target crank angle range, but also the alternator 34 is driven to generate electric power to possibly cause unnecessary operation of the alternator 34, for example, overcharging of the battery 35, or the like.
In consideration of this point, the ECU 41 according to the present embodiment compares the required load torque Td with the maximum load torque Tmax of the alternator 34 at the engine rotational speed NE at that time, and, when the ECU 41 determines that the required load torque Td is larger than the maximum load torque Tmax of the alternator 34, the ECU 41 ends the stop position control.
Next, the procedure of the stop position control executed by the ECU 41 according to the present embodiment will be described with reference to the flowchart shown in FIG. 7. A series of processes shown in the flowchart in the drawing are repeatedly executed by the ECU 41 immediately after the internal combustion engine 11 is started.
In the above series of processes, the ECU 41 first determines whether the above described predetermined stop condition is satisfied and then an engine stop request is issued (step S1). When no engine stop request is issued (NO in step S1), the ECU 41 ends the process. On the other hand, when an engine stop request is issued (YES in step S1), the ECU 41 calculates a target rotational behavior (step S2), and, subsequently, calculates a required load torque Td (step S3).
Next, the specific procedure of calculating a target rotational behavior in step S2 will be described with reference to the flowchart shown in FIG. 8. The ECU 41 first determines whether a target rotational behavior calculation completion flag Fa is set at "0" (step S2-1). Note that the target rotational behavior calculation completion flag Fa is set at "0" before a target rotational behavior is calculated, and is set at "1" when calculation of a target rotational behavior is completed. When the target rotational behavior calculation completion flag Fa is not set at "0" (NO in step S2-1), the ECU 41 ends the process.
On the other hand, when the target rotational behavior calculation completion flag Fa is set at "0" (YES in step S2-1), the ECU 41 uses the mathematical expression (1) to calculate the square of a target engine rotational speed NEtg(i+1) (step S2-2). After that, the ECU 41 determines whether the square of the target engine rotational speed NEtg(i+1) is larger than the square of a maximum engine rotational speed NEmax at or below which stop position control is executable (step S2-3). Then, when the square of the target engine rotational speed NEtg(i+1) is smaller than or equal to the square of the maximum engine rotational speed NEmax (NO in step S2-3), the ECU 41 maintains the target rotational behavior calculation completion flag Fa at "0" (step S2-4).
Subsequently, the ECU 41 subtracts 30CA, which is a calculation interval, from the current crank angle θ(i) to calculate the next crank angle θ(i+1) (step S2-5), and then determines whether the next crank angle θ(i+1) is "-30" (step S2-6). Then, when the next crank angle θ(i+1) is "-30" (YES in step S2-6), the ECU 41 determines that the next crank angle θ(i+1) crosses TDC, and proceeds to step S2-7. In step S2-7, the ECU 41 updates the next crank angle θ(i+1) to "ATDC150", and increments the number of times n TDC is passed until the target crank angle is reached (n = n+1), and then proceeds to step S2-8.
On the other hand, when it is determined in step S2-6 that the next crank angle θ(i+1) is not "-30" (NO in step S2-6), the ECU 41 determines that the next crank angle θ(i+1) does not cross TDC yet, and proceeds to step S2-8 without changing the next crank angle θ(i+1) calculated in step S2-5.
In step S2-8, the square root of the square of the target engine rotational speed NEtg(i+1) calculated in step S2-2 is calculated to obtain the target engine rotational speed NEtg(i+1), and the obtained target engine rotational speed NEtg(i+1) is allocated to the table of the target rotational behavior shown in FIG. 3. Then, the ECU 41 ends the process.
Then, the ECU 41 repeats the above processes. When the square of the target engine rotational speed NEtg(i+1) is larger than the square of the maximum engine rotational speed NEmax (YES in step S2-3), the ECU 41 sets the target rotational behavior calculation completion flag Fa at "1" (step S2-9), and proceeds to step S2-8. Thereafter, the ECU 41 completes calculation of the target rotational behavior and ends the process.
Next, the specific procedure of calculating a required load torque Td in step S3 of FIG. 7 will be described with reference to the flowchart shown in FIG. 9. First, the ECU 41 loads the crank angle θ and the engine rotational speed NE through signals detected by the various sensors (step S3-1), and determines whether the current crank angle θ is a timing (any one of 0, 30, 60, 90, 120 and 150CA at the intake ATDC) at which the load torque of the alternator 34 is controlled (step S3-2). Then, when the current crank angle θ is not a timing at which the load torque of the alternator 34 is controlled (NO in step S3-2), the ECU 41 ends the process.
On the other hand, when the current crank angle θ is a timing at which the load torque of the alternator 34 is controlled (YES in step S3-2), the ECU 41 determines whether the current engine rotational speed NE is lower than the maximum engine rotational speed NEmax (step S3-3). Then, when the current engine rotational speed NE is higher than or equal to the maximum engine rotational speed NEmax (NO in step S3-3), the ECU 41 ends the process.
In contrast, when the current engine rotational speed NE is lower than the maximum engine rotational speed NEmax (YES in step S3-3), the ECU 41 determines whether a control start value setting completion flag Fb is set at "0" (step S3-4). Note that the control start value setting completion flag Fb is set at "0" before a value of the number of calculations i at the beginning of control (control start value), and is set at "1" when the control start value of the number of calculations i is set.
Here, when the control start value setting completion flag Fb is set at "0" (YES in step S3-4), the ECU 41 sets the control start value of the number of calculations i (step S3-5). To set the control start value of the number of calculations i, the ECU 41 refers to the table of the target rotational behavior shown in FIG. 3, and sets the value of the number of calculations i, at which the crank angle θ and the target engine rotational speed NEtg are closest to the current crank angle θ and engine rotational speed NE, as the control start value.
After that, the ECU 41 sets the control start value setting completion flag Fb at "1" (step S3-6). Subsequently, the ECU 41 refers to the table of the target rotational behavior shown in FIG. 3, and sets the target engine rotational speed NEtg(i), corresponding to the control start value of the number of calculations i, to the control start value at the target engine rotational speed NEtg in the current stop position control (step S3-7), and then proceeds to step S3-8. Note that when the control start value setting completion flag Fb is set at "1" (NO in step S3-4), the ECU 41 proceeds to step S3-8 without executing the processes in steps S3-5 to S3-7.
Then, in step S3-8, the ECU 41 uses the current engine rotational speed NE, the target engine rotational speed NEtg(i) and the reference load torque Tref(NE) of the alternator 34 to calculate the required load torque Td on the basis of the mathematical expression (2) (step S3-8). After that, the ECU 41 decrements the value of the number of calculations i (step S3-9: i = i-1), and sets the target engine rotational speed NEtg(i-1) used to calculate the required load torque Td after a variation in Δθ (30CA), and then ends the process.
In this way, when the required load torque Td is calculated in step S3, the ECU 41 proceeds to step S4 shown in FIG. 7, and calculates the maximum load torque Tmax of the alternator 34 at the current engine rotational speed NE on the basis of the map shown in FIG. 5 (step S4). Then, the ECU 41 determines whether the required load torque Td is smaller than or equal to the maximum load torque Tmax (step S5).
When the required load torque Td is smaller than or equal to the maximum load torque Tmax (YES in step S5), the ECU 41 multiplies the required load torque Td by the pulley ratio to calculate the required shaft torque Tdf of the alternator 34 (step S6) and then detects the voltage of the battery 35 (step S7). Subsequently, as shown in FIG. 6, the ECU 41 selects a required load torque characteristic map corresponding to the current battery voltage from among a plurality of required load torque characteristic maps generated respectively for battery voltages as shown in FIG. 6, and calculates a power generation instruction corresponding to the current required shaft torque Tdf and engine rotational speed NE. Then, the ECU 41 controls the power generation control current of the alternator 34 on the basis of the power generation instruction to control the load torque of the alternator 34 (step S8).
After that, the ECU 41 determines whether the current engine rotational speed NE is lower than a power generation limit rotational speed NElow at or above which the load torque of the alternator 34 is controllable (step S9), and, when the engine rotational speed NE is higher than or equal to the power generation limit rotational speed NElow (NO in step S9), the ECU 41 returns to step S2. Then, when the engine rotational speed NE is lower than the power generation limit rotational speed NElow (YES in step S9), the ECU 41 stops power generation control current to the alternator 34, and ends the series of processes.
On the other hand, when the engine rotational speed NE exceeds the target engine rotational speed NEtg because of the above described various reasons to cause a large gap between the engine rotational speed NE and the target engine rotational speed NEtg and, as a result, the required load torque Td becomes larger than the maximum load torque Tmax (NO in step S5), the ECU 41 stops power generation control current to the alternator 34 irrespective of the engine rotational speed NE (step S10), and then ends the series of processes. Thus, when it is impossible to stop the engine at the crank angle θ that falls within the target crank angle range even when the load torque of the alternator 34 is controlled, the ECU 41 ends the stop position control. Hence, it is possible to prevent unnecessary operation of the alternator 34, such as overcharging of the battery 35.
As described above, according to the present embodiment, the following advantageous effects are obtained.

(1) When the internal combustion engine 11 is stopped, the ECU 41 controls the load torque of the alternator 34 so that the engine rotational speed NE coincides with the target engine rotational speed NEtg. By so doing, the ECU 41 executes stop position control in which the internal combustion engine 11 is stopped at the crank angle θ that falls within the target crank angle range. While the stop position control is being executed, the ECU 41 calculates a required load torque Td necessary to make the engine rotational speed NE coincide with the target engine rotational speed NEtg, and then compares the required load torque Td with the maximum load torque Tmax of the alternator 34 at the engine rotational speed NE at that time. Then, when the required load torque Td is larger than the maximum load torque Tmax, the ECU 41 ends the stop position control.

Therefore, the ECU 41 ends the stop position control when it is impossible to stop the engine at the crank angle θ that falls within the target crank angle range even when the load torque of the alternator 34 is controlled by executing the stop position control. Thus, it is possible to prevent unnecessary operation of the alternator 34. As a result, it is possible to prevent, for example, overcharging of the battery 35 due to unnecessary operation of the alternator 34.
(2) The ECU 41 executes automatic stop-restart control in which the internal combustion engine 11 is automatically stopped when a predetermined stop condition is satisfied, and the internal combustion engine 11 is automatically restarted when a predetermined restart condition is satisfied. Therefore, when a predetermined stop condition is satisfied, such as when the vehicle is stopped, control for automatically stopping the internal combustion engine 11, so-called idling stop, is executed. Thus, the stop position control is frequently executed. In terms of this point, the ECU 41 according to the present embodiment ends the stop position control when the required load torque Td is larger than the maximum load torque Tmax, so it is possible to appropriately prevent unnecessary operation of the alternator 34.
Note that the present embodiment may be modified into the following alternative embodiments.
In the above embodiment, the alternator 34 is used as an auxiliary equipment of which the load torque is controlled; however, the auxiliary equipment is not limited to the alternator 34. For example, the load torque of another auxiliary equipment, such as a compressor of an air conditioner, may be controlled. In addition, the aspect of the invention may be applied to a vehicle that includes the internal combustion engine 11 and an electric motor as power sources, that is, a so-called hybrid vehicle, and the electric motor may be used as the auxiliary equipment.
In the above embodiment, only the alternator 34 is used as the auxiliary equipment of which the load torque is controlled; however, the number of auxiliary equipments of which the load torque is controlled is not limited to one. For example, the load torques of a plurality of auxiliary equipments, such as the alternator 34 and a compressor of an air conditioner, may be controlled.
In the above embodiment, a target rotational behavior is calculated when a predetermined stop condition is satisfied, and the load torque of the alternator 34 is then controlled; however, the aspect of the invention is not limited to this configuration. For example, the load torque of the alternator 34 may be controlled when an ignition is turned off, that is, when the engine is normally stopped.
In the above embodiment, the aspect of the invention is applied to the internal combustion engine 11 that executes automatic stop-restart control; however, the aspect of the invention is not limited to this configuration. The aspect of the invention may also be applied to an internal combustion engine that does not execute automatic stop-restart control.

Claims

A controller for an internal combustion engine (11), which includes: target rotational behavior calculation means (41) that calculates a target rotational behavior of the internal combustion engine until the internal combustion engine stops at a crank angle that is equal to a target crank angle; and stop position control means (41) that executes stop position control in which, when the internal combustion engine is stopped, a load torque of an auxiliary equipment of the internal combustion engine is controlled so that an actual rotational behavior of the internal combustion engine coincides with the target rotational behavior, and the internal combustion engine is stopped so that the crank angle falls within a target crank angle range, characterized in that:
the stop position control means includes comparing means that compares a required load torque, necessary to make the actual rotational behavior of the internal combustion engine coincide with the target rotational behavior, with a maximum load torque of the auxiliary equipment at an operating state of the internal combustion engine when the stop position control is executed, and, the stop position control means ends the stop position control when the comparing means determines that the required load torque is larger than the maximum load torque of the auxiliary equipment.
The controller for an internal combustion engine according to claim 1, wherein the auxiliary equipment comprises an alternator (34) that is driven by the internal combustion engine to generate electric power.
The controller for an internal combustion engine according to claim 1 or 2, further comprising automatic stop-restart control means that automatically stops the internal combustion engine when a predetermined stop condition is satisfied and that automatically restarts the internal combustion engine when a predetermined restart condition is satisfied.
The controller for an internal combustion engine according to any one of claims 1 to 3, wherein the internal combustion engine is used for a vehicle, and the auxiliary equipment includes a compressor of a vehicle air conditioner.
A vehicle characterized by comprising the controller for an internal combustion engine according to any one of claims 1 to 4.
A method of controlling an internal combustion engine, which includes: a target rotational behavior calculation step of calculating a target rotational behavior of the internal combustion engine until the internal combustion engine stops at a crank angle that is equal to a target crank angle; and a stop position control step of executing stop position control in which, when the internal combustion engine is stopped, a load torque of an auxiliary equipment of the internal combustion engine is controlled so that an actual rotational behavior of the internal combustion engine coincides with the target rotational behavior, and the internal combustion engine is stopped so that the crank angle falls within a target crank angle range, characterized in that:
the stop position control step includes a comparing step of comparing a required load torque, necessary to make the actual rotational behavior of the internal combustion engine coincide with the target rotational behavior, with a maximum load torque of the auxiliary equipment at an operating state of the internal combustion engine at that time; and a step of ending the stop position control when it is determined through the comparing step that the required load torque is larger than the maximum load torque of the auxiliary equipment.