JP4631775B2 - Stop position control device for internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine stop position control device, and more particularly, as an apparatus for controlling an internal combustion engine to which control for automatically stopping and restarting an internal combustion engine is applied when a vehicle is temporarily stopped. The present invention relates to a suitable stop position control device for an internal combustion engine.

  Conventionally, for example, Patent Document 1 discloses a technique for avoiding an abrupt change in a correction value (learning value) of a fuel injection amount due to a change in an operating state of an internal combustion engine. In this conventional technique, when the absolute value of the difference between the previous learning value and the current learning value exceeds a predetermined value, the amount of change from the previous learning value to the current learning value is limited. At the same time as the restriction, learning update is prohibited or the learning update speed is reduced so that the update is not performed based on an incorrect correction value.

JP-A-8-144831

  Incidentally, there is known a control for automatically stopping and restarting an internal combustion engine when a vehicle is temporarily stopped. When such control is performed, it is required to accurately control the crank stop position at the start and stop of the internal combustion engine so that the next restart can be performed smoothly. In such a case, the crank stop position at the time of automatic stop of the internal combustion engine is greatly affected by friction inside the internal combustion engine. Therefore, it is necessary to estimate the friction with high accuracy.

  For example, when the oil for lubricating the internal combustion engine is changed, the characteristics of the friction change greatly. In order to maintain highly accurate control of the crank stop position, when such a large change in the friction characteristic is recognized, it is necessary to immediately learn the change. However, the above-described conventional technique mainly focuses on avoiding a rapid change in the correction value, that is, slowing down the learning speed. For this reason, with the above-described conventional technique, when the value to be learned (friction) changes suddenly, the request cannot be satisfied in the stop position control of the internal combustion engine that requires quick learning.

  The present invention has been made to solve the above-described problems, and provides a stop position control device for an internal combustion engine that can quickly perform appropriate learning of friction even when the friction characteristic changes greatly. The purpose is to provide.

A first invention is a stop position control device for an internal combustion engine,
A friction model for calculating the friction of the internal combustion engine;
Friction learning means for calculating a friction learning value so that the calculated value of the friction model matches the actual measured value of friction;
Forgetting factor setting means for setting a forgetting factor that changes depending on the running state of the vehicle;
A friction characteristic change determination means for determining whether the characteristics change in friction occurs,
Learning value erasure amount setting means for setting an erasure amount of the friction learning value according to the forgetting factor set according to a running state when the characteristic change occurs in friction;
Learning value erasing means for erasing the friction learning value by the erasure amount set by the learning value erasure amount setting means when the characteristic change occurs in friction;
It is characterized by providing.

  The second invention is characterized in that, in the first invention, the erasure amount is set so as to decrease as the travel distance and / or travel time increases.

Further, the third invention is the crank stop position calculating means for calculating an estimated value of the crank stop position based on the predetermined parameter including the friction in the first or second invention,
A crank stop position actual value acquisition means for acquiring an actual value of the crank stop position;
Crank stop position error calculating means for calculating a crank stop position error between the estimated value of the crank stop position and the actually measured value;
The learning value erasing unit includes an erasing amount correcting unit that corrects the erasing amount so that the crank stop position error is a predetermined value or less.

  According to the first invention, when a change in the characteristics of the friction is recognized, it is possible to avoid the need to re-learn the learning from the beginning. It is possible to avoid that the initial variation such as is uniformly erased. For this reason, according to the present invention, even when the friction characteristic changes greatly, appropriate learning of friction can be quickly executed.

  According to the second aspect of the invention, the amount of elimination of the friction learning value is changed in accordance with the travel distance and / or travel time, so that the change in the friction characteristics can be accommodated while leaving the secular change and the machine difference variation. Quick friction learning can be performed.

  According to the third aspect of the present invention, the friction learning value can be quickly optimized so that the crank stop position error can be sufficiently reduced only by adjusting the erase amount of the friction learning value.

Embodiment 1 FIG.
[Configuration of Device of Embodiment 1]
FIG. 1 is a diagram for explaining the configuration of an internal combustion engine 10 to which the stop position control device for an internal combustion engine according to the first embodiment of the present invention is applied. The system of this embodiment includes an internal combustion engine 10. Here, it is assumed that the internal combustion engine 10 is an in-line four-cylinder engine. A piston 12 is provided in the cylinder of the internal combustion engine 10. The piston 12 is connected to the crankshaft 16 via a connecting rod 14. A combustion chamber 18 is formed in the cylinder of the internal combustion engine 10 on the top side of the piston 12. An intake passage 20 and an exhaust passage 22 communicate with the combustion chamber 18.

  A throttle valve 24 is provided in the intake passage 20. The throttle valve 24 is an electronically controlled throttle valve that can control the throttle opening independently of the accelerator opening. In the vicinity of the throttle valve 24, a throttle position sensor 26 for detecting the throttle opening degree TA is disposed. A fuel injection valve 28 for injecting fuel into the intake port of the internal combustion engine 10 is disposed downstream of the throttle valve 24. A spark plug 30 is attached to each cylinder head of the internal combustion engine so as to protrude from the top of the combustion chamber 18 into the combustion chamber 18 for each cylinder. The intake port and the exhaust port are respectively provided with an intake valve 32 and an exhaust valve 34 for bringing the combustion chamber 18 and the intake passage 20 or the combustion chamber 18 and the exhaust passage 22 into a conductive state or a cut-off state.

  The intake valve 32 and the exhaust valve 34 are driven by an intake variable valve operating (VVT) mechanism 36 and an exhaust variable valve operating (VVT) mechanism 38, respectively. The variable valve mechanisms 36 and 38 open and close the intake valve 32 and the exhaust valve 34 in synchronization with the rotation of the crankshaft, and change their valve opening characteristics (valve opening timing, operating angle, lift amount, etc.). can do.

  The internal combustion engine 10 includes a crank angle sensor 40 in the vicinity of the crankshaft. The crank angle sensor 40 is a sensor that reverses the Hi output and the Lo output each time the crankshaft rotates by a predetermined rotation angle. According to the output of the crank angle sensor 40, the rotational position of the crankshaft and its rotational speed (engine rotational speed Ne) can be detected. The internal combustion engine 10 also includes a cam angle sensor 42 in the vicinity of the intake camshaft. The cam angle sensor 42 is a sensor having the same configuration as the crank angle sensor 40. According to the output of the cam angle sensor 42, the rotational position (advance amount) of the intake cam shaft can be detected.

  The system shown in FIG. 1 includes an ECU (Electronic Control Unit) 50. In addition to the various sensors described above, an ECU 50 is connected to an air-fuel ratio sensor 52 for detecting the exhaust air-fuel ratio in the exhaust passage 22 and a water temperature sensor 54 for detecting the cooling water temperature of the internal combustion engine 10. In addition, the above-described various actuators are connected to the ECU 50. The ECU 50 can control the operation state of the internal combustion engine 10 based on the sensor output and the calculation result using the engine model 60 virtually configured in the ECU 50.

[Overview of engine model]
FIG. 2 is a block diagram showing the configuration of the engine model 60 provided in the ECU 50 shown in FIG. As shown in FIG. 2, the engine model 60 includes a motion equation calculation unit 62 around the crankshaft 62, a friction model 64, an intake pressure estimation model 66, an in-cylinder pressure estimation model 68, a combustion waveform calculation unit 70, a large An atmospheric pressure correction term calculation unit 72 and an atmospheric temperature correction term calculation unit 74 are included. Hereinafter, a detailed configuration of each part will be described.

(1) About the equation of motion calculation unit around the crankshaft The equation of motion calculation unit 62 around the crankshaft is used to obtain respective estimated values of the crank angle θ and the engine speed Ne (crank angle rotational speed dθ / dt). It is. The motion equation calculation unit 62 around the crankshaft receives an input of the in-cylinder pressure P of the internal combustion engine 10 from the in-cylinder pressure estimation model 68 or the combustion waveform calculation unit 70, and at the start of the calculation, further includes the initial crank angle θ ₀ and the initial engine. Receives input of rotation speed Ne ₀ .

  The estimated crank angle θ and the estimated engine speed Ne calculated by the motion equation calculation unit 62 around the crankshaft are eliminated from the actual crank angle θ and the actual engine speed Ne by the PID controller 76 shown in FIG. Is feedback controlled. In addition, the calculation result of the motion equation calculation unit 62 around the crankshaft is reflected by the friction model 64 on the influence on the internal friction of the internal combustion engine 10.

Next, specific calculation contents executed inside the motion equation calculation unit 62 around the crankshaft will be described.
FIG. 3 is a diagram showing symbols attached to each element around the crankshaft. As shown in FIG. 3, here, A is the surface area of the top of the piston 12 that receives the in-cylinder pressure P. The length of the connecting rod 14 is L, and the crank radius is r. An angle formed by an imaginary line (cylinder axis) connecting the piston attachment point of the connecting rod 14 and the axial center of the crankshaft 16 and the axis of the connecting rod 14 is φ (hereinafter referred to as “connecting rod angle φ”). The angle formed by the cylinder axis and the axis of the crankpin 17 is defined as θ.

In the internal combustion engine 10 having four cylinders, the phase difference of the crank angle between the cylinders is 180 ° CA. Therefore, the relationship of the crank angle between the cylinders can be defined as the following equation (1a). it can. Further, the crank angle rotational speed dθ / dt of each cylinder is a time derivative of the crank angle θ of each cylinder, and can be expressed as the following equation (1b).

  However, in the above formulas (1a) and (1b), the reference numerals 1 to 4 given to the crank angle θ and the crank angle rotational speed dθ / dt are the cylinders in which combustion arrives according to the predetermined explosion order of the internal combustion engine 10. These numbers correspond to the order, and in the mathematical formulas described later, those symbols 1 to 4 may be represented by “i”.

ただし、上記（２）式において、dXi/dtはピストン速度である。 In the piston / crank mechanism shown in FIG. 3, the crank angle θi and the connecting rod angle φi have a relationship represented by the following equation (2).

However, in the above equation (2), dXi / dt is the piston speed.

Further, the total kinetic energy T around the crankshaft can be expressed as the following equation (3). When formula (3) is expanded, various parameters of each term in formula (3) can be collected as a coefficient of 1/2 (dθ / dt) ² . Here, the coefficients summarized in this way are expressed as a function f (θ) of the crank angle θ.

However, in the above equation (3), the first term on the right side is the kinetic energy related to the rotational motion of the crankshaft 16, the second term on the right side is the kinetic energy related to the linear motion of the piston 12 and the connecting rod 14, and the third term on the right side is the connecting rod 14. Respectively corresponding to the kinetic energy related to the rotational motion of the. In the above equation (3), I _k is the moment of inertia around the axis of the crankshaft 16, I _fl is the moment of inertia around the rotation axis of the flywheel, and I _mi is the transmission combined with the internal combustion engine 10. The following is the moment of inertia around the rotation axis of the rotating part, and I _c is the moment of inertia related to the connecting rod. Also, m _p is the displacement of the piston 12, m _c is the displacement of the connecting rod 14.

Next, Lagrangian L is defined as the following equation (4a) as the deviation between the total kinetic energy T and the potential energy U of the system. If the input torque acting on the crankshaft 16 is TRQ, the relationship between the Lagrangian L, the crank angle θ, and the input torque TRQ can be expressed by the following equation (4b) using the Lagrangian equation of motion. it can.

  Here, in the above equation (4a), the influence of the potential energy U is smaller than the influence of the kinetic energy T, and the influence can be ignored. Therefore, the first term on the left side of the equation (4b) is a function of the crank angle θ by differentiating the value obtained by partial differentiation of the equation (3) with respect to the crank angle rotation speed (dθ / dt). Can be expressed as the following equation (4c). Further, the second term on the left side of the above equation (4b) can be expressed as the following equation (4d) as a function of the crank angle θ by partially differentiating the above equation (3) with respect to the crank angle θ. .

Therefore, the above equation (4b) can be expressed as the following equation (4e), whereby the relationship between the crank angle θ and the input torque TRQ can be obtained. Further, here, the input torque TRQ is defined as consisting of three parameters as shown in the following equation (5).

However, in the above equation (5), TRQ _e is the engine generated torque, more specifically, the torque acting on the crankshaft 16 from the piston 12 that receives the gas pressure (in-cylinder pressure P). TRQ _L is a load torque, and is stored in the ECU 50 as a known value that varies depending on the characteristics of the vehicle on which the internal combustion engine 10 is mounted. TRQ _f is a friction torque, that is, a torque corresponding to a friction loss of sliding portions such as the piston 12 and the crankshaft 16. This friction torque TRQ _f is a value obtained from the friction model 64.

Next, the engine generated torque TRQ _e can be calculated according to the following equations (6a) to (6c). That is, first, the force F _c acting on the connecting rod 14 based on the in-cylinder pressure P can be expressed as the equation (6a) as the axial component of the connecting rod 14 of the force PA acting on the top of the piston 12. . As shown in FIG. 3, the angle α formed between the axis of the connecting rod 14 and the tangent to the locus of the crankpin 17 is {π / 2− (φ + θ)}. The force F _k acting in the tangential direction of the trajectory can be expressed as the equation (6b) using the force F _c acting on the connecting rod 14. Therefore, since the engine generated torque TRQ _e is the product of the force F _k acting in the tangential direction of the locus of the crank pin 17 and the rotation radius r of the crank, using the equations (6a) and (6b), 6c) can be expressed as:

  According to the configuration of the motion equation calculation unit 62 around the crankshaft described above, the in-cylinder pressure P is acquired by the in-cylinder pressure estimation model 68 or the combustion waveform calculation unit 70, whereby the equations (6c) and (5) are obtained. Input torque TRQ can be obtained. Then, by solving the equation (4e), it is possible to obtain the crank angle θ and the crank angle rotation speed dθ / dt.

(2) About Friction Model FIG. 4 shows an example of a friction map provided for the friction model 64 shown in FIG. 2 to acquire the friction torque TRQ _f . In the friction map shown in FIG. 4, the friction torque TRQ _f is determined by the relationship between the engine speed Ne and the engine coolant temperature. Such a characteristic of the friction map is determined in advance by experiments or the like, and the friction torque TRQ _f tends to increase as the engine coolant temperature decreases.

ただし、上記（７）式において、C₁、C₂、C₃は、それぞれ実験等により適合される係数である。 Here, in order to reduce the calculation load of the ECU 50, the friction model 64 is provided with the friction map as described above, but the configuration of the friction model is not limited to this, and the following A relational expression such as the expression (7) may be used. In the equation (7), the friction torque TRQ _f is configured to be a function having the engine speed Ne and the kinematic viscosity ν of the lubricating oil of the internal combustion engine 10 as parameters.

However, in the above equation (7), C ₁ , C ₂ , and C ₃ are coefficients that are adapted by experiments or the like.

(3) Intake Pressure Estimation Model The intake pressure estimation model 66 includes an intake pressure map (not shown) for estimating the intake pressure. This intake pressure map defines the intake pressure in relation to the throttle opening degree TA, the engine speed Ne, and the valve timing VVT of the intake and exhaust valves. According to such a configuration of the intake pressure estimation model, it is possible to acquire the intake pressure while keeping the calculation load of the ECU 50 low. When the intake pressure is calculated in detail, a throttle model that estimates the air flow rate that passes through the throttle valve 24 and the air flow rate that passes around the intake valve 32 without using the intake pressure map as described above. An intake pressure estimation model may be configured using a valve model that estimates (in-cylinder intake air flow rate).

(4) In-cylinder pressure estimation model The in-cylinder pressure estimation model 68 is a model used to calculate the in-cylinder pressure P under a situation where combustion is not performed. In this in-cylinder pressure estimation model 68, the in-cylinder pressure P in each stroke of the internal combustion engine 10 is calculated using the following equations (8a) to (8d). That is, first, the in-cylinder pressure P during the intake stroke is obtained from the in-cylinder pressure map value P _map obtained from the intake pressure map of the intake pressure estimation model 66 described above, as shown by the equation (8a). I am doing so.

Next, the in-cylinder pressure P during the course of the compression stroke can be expressed as in equation (8b) based on the equation for reversible adiabatic change of gas.
However, in the above equation (8b), V _BDC is the stroke volume V when the piston 12 is at the intake bottom dead center, and κ is the specific heat ratio.

Further, the in-cylinder pressure P during the expansion stroke can also be expressed as in the equation (8c) in the same manner as in the compression stroke.
However, in the above equation (8c), V _TDC is the stroke volume V when the piston 12 is at the compression top dead center, and P _c is the in-cylinder pressure at the end of the compression stroke.

Further, the in-cylinder pressure P during the exhaust stroke is assumed to be the pressure P _ex in the exhaust passage 22 as shown by the equation (8d). This pressure P _ex can be regarded as substantially equal to the atmospheric pressure P _air . Therefore, here, the atmospheric pressure P _air is used as the in-cylinder pressure P during the exhaust stroke.

(5) Combustion waveform calculation unit The combustion waveform calculation unit 70 is a model used to calculate the in-cylinder pressure (combustion pressure) P during the period in which combustion is performed from the middle of the compression stroke to the middle of the expansion stroke. It is. In the combustion waveform calculation unit 70, an estimated value of the combustion pressure P is calculated using an equation (9a) that is a relational expression using the Weibe function and an equation (10) described later.

More specifically, the combustion waveform calculation unit 70 first calculates the heat generation rate dQ / dθ corresponding to the current crank angle θ using the equation (9a).
However, in the above equation (9a), m is the shape factor, k is the combustion efficiency, θ _b is the ignition delay period, and a is the combustion rate (here, fixed value 6.9). For each of these parameters, pre-adapted values are used. Q is the calorific value.

  In order to calculate the heat generation rate dQ / dθ using the above equation (9a), it is necessary to calculate the calorific value Q. The calorific value Q can be calculated by solving the equation (9a) which is a differential equation. Therefore, first, in the equation (9b), the part corresponding to the Weibe function in the equation (9a) is replaced with g (θ). If it does so, it will become possible to express (9a) Formula like (9c) Formula. Next, after integrating both sides of the formula (9c) with the crank angle θ, the calorific value Q can be expressed as the formula (9d) by developing the formula (9c). Next, the heat generation rate dQ / dθ is calculated by substituting the calorific value Q calculated according to the equation (9d) into the equation (9a) again.

The heat release rate dQ / dθ and the in-cylinder pressure (combustion pressure) P can be expressed as in equation (10) using a relational expression based on the law of conservation of energy. Therefore, the combustion pressure P can be calculated by substituting the heat release rate dQ / dθ calculated according to the equation (9a) and solving the equation (10).

  According to the in-cylinder pressure estimation model 68 and the combustion waveform calculation unit 70 described above, the in-cylinder pressure P is calculated using the in-cylinder pressure estimation model 68 in a state where combustion is not performed, and the combustion waveform calculation unit 70 is calculated. By calculating the in-cylinder pressure P during the period during which combustion is performed, the history of the in-cylinder pressure P of the internal combustion engine 10 can be acquired regardless of whether combustion is performed.

In addition, the method of acquiring the history of the in-cylinder pressure P of the internal combustion engine 10 is not limited to the above method, and may be a method as shown with reference to FIG.
FIG. 5 is a diagram for explaining a method of such a modification. In this method, the combustion pressure P is not calculated for each predetermined crank angle θ using the above equations (9a) and (10), but the above equations (9a) and (10) are calculated in advance. Using the equation, only the combustion pattern as shown in FIG. 5A, that is, the change in the waveform of the in-cylinder pressure P that changes as a result of being applied to combustion (the pressure increase due to combustion) is calculated in advance. .

More specifically, there are three parameters that determine such a combustion pattern: ignition delay period, combustion period, and ΔP _max (deviation between maximum pressure P _max during combustion and maximum pressure P _max0 without combustion). Are stored in relation to the engine speed Ne, the air filling rate KL, the valve timing VVT of the intake and exhaust valves, and the ignition timing. Then, in order to calculate the waveform corresponding to the pressure increase due to combustion as a waveform approximated by combining simple functions such as a quadratic function, each coefficient of the approximate waveform is related to the engine speed Ne. Map it with. Then, as shown in FIG. 5B, the waveform of the pressure increase due to combustion obtained by referring to such a map is added to the value of the in-cylinder pressure P calculated by the in-cylinder pressure estimation model 68. Thus, the combustion pressure P is acquired.

(6) The atmospheric pressure correction term calculation unit atmospheric pressure correction term calculation unit 72, a model for estimating the in-cylinder charged air amount M _c is taken into the cylinder (referred to herein as "air model") contains. In this air model, it has decided to calculate the in-cylinder charged air amount M _c according to the following equation (11).

However, in the above equation (11), a and b are coefficients adapted according to operating conditions (engine speed Ne, valve timing VVT, etc.), respectively. Note that P _m is the intake pressure, and for example, a value calculated by the intake pressure estimation model 66 described above can be used.

Further, the atmospheric pressure correction term calculation unit 72 (here referred to as "fuel model") model for estimating the fuel quantity f _c drawn into the cylinder contains. Considering the behavior of the fuel after being injected from the fuel injection valve 28, that is, taking into account the phenomenon of part of the injected fuel adhering to the inner wall of the intake port and the vaporization of the adhering fuel, the k-th cycle When the fuel adhering to the wall surface at the start of fuel injection is f _w (k) and the actual fuel injection amount in the k-th cycle is f _i (k), the wall surface adhering after the end of the k-th cycle The fuel amount f _w (k + 1) and the fuel amount f _c sucked into the cylinder in the k-th cycle can be expressed as the following equations (12a) and (12b).

However, in the above (12), P is, deposition rate, and more specifically, the ratio of the amount of fuel adhering to the inner wall of the intake port of the fuel injection amount f _i. R is the residual percentage, more specifically, adherent fuel amount f _w after execution of the intake stroke is the fraction that remains in a state adhered to the wall surface or the like.
According to the above (12), the adhesion rate P and the residual rate R as a parameter, it is possible to calculate the fuel quantity f _c for each individual cycle.

Therefore, the estimated value of the air-fuel ratio A / F can be calculated using the calculation results of the air model and the fuel model. Next, the atmospheric pressure correction term calculation unit 72 detects the estimated air / fuel ratio A / F and the air / fuel ratio detected at a timing considering the transport delay until the injected fuel reaches the air / fuel ratio sensor 52 after being subjected to combustion. The steady deviation from the actual measurement value of the fuel ratio A / F is calculated. Then, the steady state error for the error of the in-cylinder charged air amount M _c, when the steady-state deviation is large, the assumption that the atmospheric pressure is deviated, calculates the atmospheric pressure correction coefficient k _airp. Specifically, calculated back to the intake pressure P _m above the air model, we calculate the atmospheric pressure correction coefficient k _airp as a correction factor for the standard atmospheric pressure P _a0 based on the intake air pressure P _m. The atmospheric pressure correction coefficient k _airp is used for correcting the intake pressure P _map and the exhaust pressure (atmospheric pressure P _air ) in the intake pressure estimation model 66 and the in-cylinder pressure estimation model 68 described above.

(7) About the atmospheric temperature correction term calculation unit In the atmospheric temperature correction term calculation unit 74, the stroke volume V during the exhaust stroke, the residual gas mass (calculated based on the clearance volume V _c at the exhaust top dead center) m, the residual gas The in-cylinder pressure P _th is calculated by substituting the measured values of the gas constant R of (burnt gas) and the atmospheric temperature T _air into the ideal gas equation of state. A deviation between the in-cylinder pressure P _th and the in-cylinder pressure P calculated by the in-cylinder pressure estimation model 68 is calculated. If the deviation is large, a correction coefficient is calculated based on the deviation. This correction coefficient is used to correct the intake pressure P _map in the intake pressure estimation model 66 described above.

[Friction model learning method]
In a vehicle including an internal combustion engine, when the vehicle temporarily stops, control (eco-run control) that automatically stops and restarts the internal combustion engine may be executed. Further, even in a hybrid vehicle that drives a vehicle with an internal combustion engine and a motor, control that automatically stops and restarts the internal combustion engine during startup of the vehicle system (including when the vehicle is running) (in this specification, This is also called “eco-run control” in a broad sense).

  In the eco-run control described above, in order to smoothly restart the internal combustion engine, the crankshaft stop position (piston stop position) when automatically stopping the internal combustion engine is accurately controlled to the target stop position. There is a demand to do. In the system of the present embodiment, the engine model 60 described above is used as a stop position estimation model for estimating the stop position of the crankshaft 16 during eco-run control. According to the engine model 60 described above, the stop position of the crankshaft 16 when the internal combustion engine 10 is automatically stopped is acquired by acquiring the estimated value of the crank angle θ when the crank angle rotation speed dθ / dt becomes zero. can do. In the present specification, the stop position of the crankshaft 16 may be simply referred to as “crank stop position”.

  The crank stop position when the internal combustion engine 10 is automatically stopped is greatly affected by friction inside the internal combustion engine 10 and the like. Therefore, it is necessary to estimate the friction with high accuracy. Therefore, the system of this embodiment includes a friction model 64 and has a configuration in which the friction is appropriately learned by adaptive control so that the calculated value of the friction model 64 matches the measured value of friction.

For example, when the oil for lubrication of the internal combustion engine 10 is changed, the characteristics of the friction change greatly. In the case where there is a large change in such friction properties, and friction torque TRQ _{F_model} the friction model 64 is calculated, friction deviation between the actual friction torque TRQ _{F_jitsu} increases temporarily. That is, a condition where the learning value of friction is greatly different may occur.

  When the above conditions occur, it is conceivable that the friction learning value is completely reset. However, if the friction learning value is completely reset, it is necessary to start learning again from the beginning. In addition, the initial variation such as the secular change of friction and the difference in machine difference learned until the reset time is also reset together. For this reason, such a method cannot respond to a quick learning execution request.

  Therefore, in the system of this embodiment, a forgetting coefficient that changes depending on the travel distance (traveling time) of the vehicle is set, and friction learning is performed when the friction characteristics change significantly according to the magnitude of the forgetting coefficient. The reset amount (erasing amount) of the value (oil deterioration friction learning value) was changed. According to such a method, it is possible to perform quick friction learning corresponding to the change of the friction characteristic while leaving the aging change of the friction learning value and the machine difference variation.

  Here, in the present embodiment, the friction learning value for correcting the friction model 64 includes an “oil deterioration friction learning value” due to the effect of oil deterioration and an “aging change and The machine difference variation friction learning value ”is assumed to be configured. Further, in the present embodiment, it is assumed that an oil deterioration friction learning value corresponds to a learning value calculated by friction learning constantly performed by the engine model 60.

Next, specific processing in the first embodiment will be described with reference to FIG.
FIG. 6 is a flowchart of a routine executed by the ECU 50 in the first embodiment to realize the above function.
(About step 100)
In the routine shown in FIG. 6, first, it is determined whether or not the operating state of the internal combustion engine 10 is in an idling state or a steady state, that is, whether or not the internal combustion engine 10 is in a stable state (step 100).

尚、（１３ｃ）式が得られる過程を説明すると、J(θ)を上記（１３ａ）式のように定めることで、上記（４ｅ）式で表されるクランク軸周りの運動方程式は、上記（１３ｂ）式のように表すことができる。そして、（１３ｂ）式の左辺が算出フリクショントルクTRQ_fとなるように書き直すことで、（１３ｃ）式を得ることができる。 (About step 102)
If it is determined in step 100 that the operating state of the internal combustion engine 10 is in a stable state, then, using the engine model 60, a predetermined map corresponding to the friction map (see FIG. 4) of the friction model 64 is used. For each rotation speed region, the average value of the friction torque TRQ _f in each rotation speed region is calculated (step 102). Here, in order to distinguish from the value obtained from the friction map, the friction torque TRQ _f calculated in this step 102 is referred to as “calculated friction torque TRQ _f ” or simply “calculated friction”. The calculated friction can be calculated according to the following equation (13c) by substituting the respective measured values of the crank angle θ and the crank angle rotation speed dθ / dt into the engine model 60.

The process of obtaining the equation (13c) will be described. By defining J (θ) as in the above equation (13a), the equation of motion around the crankshaft represented by the above equation (4e) is 13b) can be expressed as: Then, the expression (13c) can be obtained by rewriting the expression so that the left side of the expression (13b) becomes the calculated friction torque TRQ _f .

(About step 104)
Next, the friction error between the calculated friction calculated in step 102 and the friction torque TRQ _f (hereinafter referred to as “friction map value”) obtained by the friction map shown in FIG. 4 is larger than a predetermined threshold value, and Then, it is determined whether or not the absolute value of the friction map value is larger than the absolute value of the calculated friction (step 104).

The friction map value is subjected to adaptive learning so as to coincide with the actual friction torque TRQ _f . Nevertheless, if it is recognized that the above-described friction error has occurred, it can be determined that some factor that greatly changes the friction of the internal combustion engine 10 has occurred. The calculated friction is obtained as a friction torque value in which an actual value such as the crank angle θ is substituted and the current state of the internal combustion engine 10 is reflected. Therefore, when it is determined that such calculated friction is smaller than the friction map value stored as the friction model 64 being true, that is, when the determination condition of this step 104 is satisfied, the internal combustion engine It can be determined that the actual friction of 10 has decreased, that is, the oil has been changed.

(About step 106)
Next, a case where the determination condition in step 104 is not satisfied will be described first. In this case, it is next determined whether or not the friction error is larger than the threshold value and the absolute value of the calculated friction is larger than the absolute value of the friction map value (step 106).

(About step 108)
If it is determined in step 106 that a friction error larger than the threshold value is present, but the calculated friction is determined to be larger than the friction map value, the actual friction of the internal combustion engine 10 is relatively large. It can be judged. Therefore, in this case, the forgetting factor is calculated according to the travel distance at the time of the previous learning and the current travel distance (step 108). More specifically, in this step 108, the forgetting factor is calculated according to the map shown in FIG. Here, the forgetting factor is determined in relation to the travel distance of the vehicle, but the forgetting factor may be determined based on the travel time instead of the travel distance or together with the travel distance.

  FIG. 7 shows an example of a map that defines the relationship between the forgetting factor and the travel distance. In the forgetting factor map shown in FIG. 7, the forgetting factor is set so as to increase in proportion to the traveling distance until the coefficient reaches 1 when the predetermined traveling distance is reached.

(About step 110)
Next, it is determined whether or not the forgetting factor has reached 1 (step 110).
(About step 112)
As a result, if it is determined that the forgetting factor has reached 1, the friction learning value learned so far as the oil deterioration friction learning value becomes the secular change and machine difference variation friction learning value. Moved (step 112). It can be determined that the value accumulated as the oil deterioration friction learning value when the predetermined travel distance until the forgetting factor reaches 1 is not a learning value based on a sudden factor such as oil change. Then, such accumulated learning values (values corresponding to aging and machine difference variations) are determined together with the amount of oil deterioration when it is determined in step 116 described later that a factor such as oil change has occurred. It can be determined that the learning value should not be reset. For this reason, according to the process of this step 112, such an accumulated learning value can be made less susceptible to the reset in the process of step 116 described later.

In the forgetting factor map shown in FIG. 7, the traveling distance (traveling time) until the forgetting factor becomes 0 to 1 can be, for example, a traveling distance so as to include several oil change cycles. For example, it is preferable to set it to several tens of thousands km and several years if it is traveling time. According to such settings, by ensuring a sufficient travel distance (traveling time) until the forgetting factor becomes 0 to 1, the forgetting factor becomes 1 and the oil deterioration friction learning value changes over time and machine differences. When shifting to the variation friction learning value, the friction learning value corresponding to the aging of the friction can be obtained with high reliability.
(About step 114)
Next, the travel distance is reset to zero (step 114).

(About step 116)
On the other hand, if the determination condition in the above step 104 is satisfied, that is, if it is determined that a reason for significantly changing the friction characteristics of the internal combustion engine 10 such as oil exchange has occurred, then the oil deterioration friction learning value is set to ( The oil deterioration friction learning value is reset by a value multiplied by (1−forgetting factor) (step 116). The actual friction of the internal combustion engine 10 increases with the deterioration of the internal combustion engine 10 as the travel distance increases. As a result, as the travel distance increases, the friction learning value to be captured also increases. According to the setting of the forgetting coefficient shown in FIG. 7, the reset amount can be set to an appropriate amount in accordance with such a change in the friction learning value.

(About step 118)
Next, it is determined whether or not the error between the measured value of the crank stop position and the estimated value is smaller than a predetermined threshold value (step 118). The actual measured value of the crank stop position is a value detected by the crank angle sensor 40 when the internal combustion engine 10 is stopped at the latest time. The estimated value of the crank stop position is a value calculated by the engine model 60 using the oil deterioration friction learning value that has been reset by a predetermined amount by the processing in step 116. Here, first, the estimated value is calculated. An example of the technique is shown below.

Specifically, in this step 118, the average value of the combustion pressure P acquired in the idle state, the intake pressure P _map , the crank angle θ ₀ , and the engine speed (combustion cut speed) Ne ₀ (= crank angle rotation) Speed dθ ₀ / dt) is input as an initial value, and the estimated values of the crank angle θ and the crank angle rotation speed dθ / dt are sequentially calculated using the motion equation calculation unit 62 around the crankshaft. Become. Hereinafter, the specific calculation method will be described using the following equations (14) and (15). In this specification, using such a method to solve the engine model 60 in the direction of the arrow shown in FIG. 2 is referred to as “forward model calculation”.

First, in the equation of motion around the crankshaft expressed by the above equation (4e), (∂f (θ) / ∂θ) ≡h (θ) and the input torque TRQ in the equation (4e) After substituting the equation (5) and discretizing the equation (4e), the following equation (14) is obtained.

Then, as described above, the crank angle θ ₀ , the crank angle rotation speed dθ ₀ / dt, and the like are given as the initial calculation values of the forward model calculation according to the above equation (14). Hereinafter, by sequentially updating the number of steps k, the estimated values of the corresponding crank angle θ and crank angle rotation speed dθ / dt are sequentially calculated. If the number of steps k = 1 is substituted into the above equation (14), it can be expressed as the following equation (15a).

When a part of the crank angle θ (k) in the above equation (15a) is rewritten to the corresponding crank angle rotation speed dθ (k) / dt, it can be expressed as the above equation (15b). When the equation (15b) is developed, the crank angle rotational speed dθ (1) / dt when the number of steps k = 1 is input as the previous time, that is, as an initial value, as in the above equation (15c). It can be expressed using the crank angle θ ₀ and the crank angle rotation speed dθ ₀ / dt. Further, by integrating the equation (15c), the crank angle θ (1) when the number of steps k = 1 can be calculated as the equation (15d).

  Then, when the above processing is repeated until the number of steps k reaches N times, that is, until the crank angle rotation speed reaches dθ (N) / dt = 0, the crank angle rotation speed dθ (N) / dt = 0. , And a crank angle θ (N) are calculated. That is, according to the above processing, the estimated values of the engine speed Ne = 0 when the internal combustion engine 10 is stopped and the crank stop position can be calculated.

(About step 120)
If it is determined in step 118 that the crank stop position error is equal to or smaller than the predetermined threshold value, the process of this routine is immediately terminated. On the other hand, it is determined that the crank stop position error is larger than the threshold value. If so, correction of the forgetting factor map shown in FIG. 7 is executed (step 120). Specifically, the inclination of the forgetting coefficient map is corrected, and the crank stop position error is recalculated in a state where the reset amount of the oil deterioration friction learning value based on the corrected forgetting coefficient is reflected. The correction of the inclination of the forgetting factor is repeatedly executed in step 118 until the crank stop position error becomes equal to or less than the threshold value.

  As described above, according to the process of step 112, when the forgetting factor becomes 1, the learning value is transferred from the oil deterioration friction learning value to the secular change and machine difference variation friction learning value. Therefore, if the correction of the inclination of the forgetting factor in the process of this step 120 is correction in a direction that increases the inclination, the forgetting factor may become 1 before reaching a sufficient travel distance. . If this happens, it can be said that it is not appropriate to transfer the oil deterioration friction learning value at the time when the forgetting factor reaches 1 after judging that it is caused by the secular change of friction. Therefore, in this step 120, when the inclination of the forgetting factor is corrected, the forgetting factor is larger than a predetermined value so that the forgetting factor does not become 1 before reaching a sufficient travel distance for executing the transfer to the secular change. By prohibiting the correction to the inclination, the correction in the direction of increasing the inclination is restricted. According to such processing, it is possible to stably obtain a friction learning value corresponding to aging with high reliability.

  According to the routine shown in FIG. 6 described above, when a forgetting factor that depends on the travel distance or the like is introduced and a large change in the friction characteristics is recognized, the oil according to the travel state of the vehicle such as the travel distance is determined. The reset amount of the deterioration friction learning value is changed. For this reason, it is possible to realize quick friction learning with respect to a large change in the friction characteristics while avoiding inadvertent resetting of the aging variation and the machine difference variation of the friction.

  In the above routine, after resetting the oil deterioration friction learning value, the crank stop position is recalculated based on the reset friction learning value, and until the crank stop position error becomes smaller than a predetermined threshold value, The reset amount is adjusted (learned) by correcting the forgetting factor. According to such processing, it is possible to quickly optimize the friction learning value so that the crank stop position error can be sufficiently reduced only by adjusting the reset amount by correcting the forgetting factor.

In the first embodiment described above, the ECU 50 executes the friction learning by adaptive control so that the calculated value of the friction model 64 matches the actual measured value of the friction, whereby the “friction learning” in the first invention is performed. The “means” executes the process of step 108, so that the “forgetting coefficient setting means” in the first invention executes the process of step 104, and the “friction characteristic change determining means in the first invention”. ”, The “ learning value erasure amount setting means ”and the “ learning value erasure means ”in the first invention are realized by executing the processing of step 116 described above.
In the first embodiment described above, the ECU 50 calculates the estimated value of the crank stop position by the method shown in step 118, so that the “crank stop position calculating means” in the third aspect of the invention is the crank angle sensor. By detecting the crank angle θ on the basis of the output of 40, the “crank stop position actual value acquisition means” in the third invention executes the processing of the above step 118, thereby executing the “crank stop in the third invention”. The “position error calculating means” executes the processing of step 120 described above, thereby realizing the “erasing amount correcting means” in the third aspect of the invention.

It is a figure for demonstrating the structure of the internal combustion engine to which the stop position control apparatus of the internal combustion engine of Embodiment 1 of this invention was applied. It is a block diagram which shows the structure of the engine model with which ECU shown in FIG. 1 is provided. It is a figure which shows the symbol attached | subjected to each element around a crankshaft. FIG. 3 is a diagram showing an example of a friction map provided for the friction model shown in FIG. 2 to acquire a friction torque TRQ _f . FIG. 6 is a diagram for explaining a modified technique for obtaining a history of in-cylinder pressure P. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows an example of the map which ECU shown in FIG. 1 has memorize | stored in order to acquire a forgetting factor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 14 Connecting rod 16 Crankshaft 24 Throttle valve 26 Throttle position sensor 40 Crank angle sensor 42 Cam angle sensor 50 ECU (Electronic Control Unit)
52 Air-fuel ratio sensor 54 Water temperature sensor 60 Engine model 62 Equation of motion calculation section around crankshaft 64 Friction model 66 Intake pressure estimation model 68 In-cylinder pressure estimation model 70 Combustion waveform calculation section 72 Atmospheric pressure correction term calculation section 74 Atmospheric temperature correction term calculation 76 PID controller
dQ / dθ Heat release rate
dθ / dt Crank angle rotation speed

Claims (3)

A stop position control device for an internal combustion engine,
A friction model for calculating the friction of the internal combustion engine;
Friction learning means for calculating a friction learning value so that the calculated value of the friction model matches the actual measured value of friction;
Forgetting factor setting means for setting a forgetting factor that changes depending on the running state of the vehicle;
A friction characteristic change determination means for determining whether the characteristics change in friction occurs,
Learning value erasure amount setting means for setting an erasure amount of the friction learning value according to the forgetting factor set according to a running state when the characteristic change occurs in friction;
Learning value erasing means for erasing the friction learning value by the erasure amount set by the learning value erasure amount setting means when the characteristic change occurs in friction;
A stop position control device for an internal combustion engine, comprising:   2. The stop position control device for an internal combustion engine according to claim 1, wherein the erasure amount is set so as to decrease as the travel distance and / or travel time increases. Crank stop position calculating means for calculating an estimated value of the crank stop position based on a predetermined parameter including the friction;
A crank stop position actual value acquisition means for acquiring an actual value of the crank stop position;
Crank stop position error calculating means for calculating a crank stop position error between the estimated value of the crank stop position and the actually measured value;
3. The stop position of the internal combustion engine according to claim 1, wherein the learning value erasing unit includes an erasing amount correcting unit that corrects the erasing amount so that the crank stop position error is equal to or less than a predetermined value. Control device.

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