JP2011252450A - Variable valve timing control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly perform valve timing control during engine restart.SOLUTION: An engine 11 includes a hydraulic variable valve mechanism 18 and a hydraulic adjusting device (OCV 31). An ECU 40 calculates a control variable of a hydraulic adjusting device using a held control variable for maintaining the current valve timing, and drives the variable valve mechanism 18 by adjusting a hydraulic pressure by the hydraulic adjusting device on the basis of the control variable. Further, on condition that a prescribed execution condition is established during the operation of the engine 11, learning about the held control variable is executed. In particular, the ECU 40 measures an engine stop time from the engine stop to a restart request, and calculates the held control variable to be used during a period after restart request until the learning execution condition is established, on the basis of the engine stop time and the learning value of the held control variable.

Description

  The present invention relates to a variable valve timing control device, and more particularly, to a variable valve timing control device that controls a variable valve mechanism that uses hydraulic pressure as a drive source and adjusts hydraulic pressure by a hydraulic pressure adjustment device.

  2. Description of the Related Art Conventionally, an engine mounted on a vehicle is known that includes a hydraulically driven variable valve mechanism that changes valve timings of an intake valve and an exhaust valve. In a hydraulically driven variable valve mechanism, an oil control valve (OCV) is controlled based on a control duty value, thereby controlling an operating hydraulic pressure supplied to the variable valve mechanism, and thereby an intake valve and an exhaust valve. Timing is changed.

  The control duty value of the OCV is based on a feedback control amount corresponding to the deviation between the target valve timing and the actual valve timing calculated based on the operating state of the engine and the holding duty value for maintaining the current valve timing. Calculated. Here, the holding duty value varies depending on the tolerance of the OCV, the temperature of the hydraulic oil, a change with time, and the like. In particular, when the engine is started, the change in oil temperature with respect to the previous operation is large.For example, if the learning value at the previous engine stop is used as it is, the holding duty value is more advanced than the actual value or more retarded. The valve timing control may not be properly performed when the engine is started. On the other hand, it is conceivable that the learning execution condition is not yet established at the time of engine start, and a new learning value cannot be acquired.

  Therefore, conventionally, various methods for calculating the holding duty value used at the time of starting the engine have been proposed (see, for example, Patent Document 1 and Patent Document 2). In Patent Document 1, when learning the holding duty value, the engine operating state amount (engine speed, oil temperature) at the time of learning is also stored. Further, it is disclosed that learning is prohibited when the engine operating state changes as in the case immediately after the engine is started, and a value obtained by correcting the previous learned value by the oil temperature or the like is used as the holding duty value.

  Further, Patent Document 2 focuses on the relationship that the holding duty value with respect to the oil temperature is high (becomes an advance value) and low (becomes a retard value) at an intermediate temperature. However, it is disclosed that the learning update of the holding duty value is allowed only when the engine temperature is on the high temperature side. That is, in Patent Document 2, when the engine is started or cold, the holding duty value learned before the engine is stopped is used as the current holding duty value. In view of the fact that there is not much difference between the holding duty value between the low temperature side and the high temperature side, by allowing learning update of the holding duty value only when the engine temperature is the high temperature side, The holding duty value used at the time is optimized.

JP-A-8-74530 Japanese Patent No. 4108789

  However, since the temperature characteristic of the holding duty value is not generally represented by a straight line (see, for example, FIG. 3), when the learning value and the oil temperature are associated with each other as in Patent Document 1, it is necessary to provide a plurality of learning regions and store them. It is conceivable that the amount of information stored in the means or the like increases. Therefore, for example, when there is a limit on the amount of information that can be stored in the storage unit, a sufficient amount of information cannot be stored. In such a case, the holding duty value cannot be set to an appropriate value according to the oil temperature. There is a fear. Moreover, in Patent Document 1, it is necessary to update the learning value for each of the plurality of learning regions, and it is considered that the learning process becomes complicated.

  Further, in Patent Document 2, when the temperature at the time of starting the engine is not as low as when cold, the valve timing is excessively advanced by using the learned value at high temperature, resulting in misfire, etc. It is feared that this will be caused. Therefore, for example, when the invention of Patent Document 2 is applied at the time of restart after the engine is stopped, the engine startability may be deteriorated due to misfire or the like. In particular, in a vehicle having an idle stop function, it is desirable to stop and restart the engine so as not to be noticed by the driver as much as possible, and it is necessary to suppress deterioration of engine startability as much as possible.

  The present invention has been made in order to solve the above-described problems, and has as its main object to provide a variable valve timing control device that can appropriately perform valve timing control when the engine is restarted.

  The present invention employs the following means in order to solve the above problems.

  The present invention includes a variable valve mechanism that adjusts valve timing on the intake side or exhaust side of an engine using hydraulic pressure as a drive source, and a hydraulic pressure adjustment device that adjusts the hydraulic pressure that drives the variable valve mechanism. Applied to an engine that is restarted in response to a start request, and adjusts the hydraulic pressure based on a feedback control amount corresponding to a deviation between a target valve timing and an actual valve timing, and a holding control amount for maintaining the current valve timing The control amount of the device is calculated, and the hydraulic pressure adjustment device adjusts the hydraulic pressure based on the control amount to drive the variable valve mechanism. On the condition that a predetermined execution condition is satisfied during operation of the engine. The present invention relates to a variable valve timing control device that learns the holding control amount.

  In the first aspect of the present invention, based on the measurement unit that measures the engine stop time from the engine stop to the restart request, the engine stop time measured by the measurement unit, and the learning value of the holding control amount. And a control amount calculating means for calculating a post-restart holding control amount that is a holding control amount used after the restart request and until the execution condition is satisfied.

  When the engine is restarted with a restart request after the engine is stopped, the holding control amount cannot be learned in the period after the restart request until the execution condition for learning the holding control amount is satisfied. A holding control amount suitable for the situation at that time cannot be acquired by learning. Therefore, it is conceivable to calculate the control amount of the hydraulic pressure adjusting device using the learned value before the engine is stopped, and to drive the variable valve mechanism based on the calculated control amount.

  Here, the holding control amount varies depending on the tolerance of the hydraulic pressure adjusting device, the temperature (oil temperature) of the hydraulic oil that drives the variable valve mechanism, changes with time, etc., and is particularly temperature-dependent. It fluctuates greatly. Further, in the engine stop period from the engine stop to the restart request, it is conceivable that the oil temperature decreases and the decrease temperature varies depending on the engine stop time. That is, when the engine is restarted, it is considered that the holding control amount differs every time depending on the engine stop time.

  In view of that, in the present invention, the execution condition for learning the hold control amount after the engine restart request is based on the engine stop time from the engine stop to the engine restart request and the learned value of the hold control amount. The holding control amount used in the period until it is established is calculated. In this way, when the engine stop time is used as a calculation parameter for the hold control amount, the oil temperature decreases while the engine is stopped, and there is a difference between the oil temperature at the time of learning and the oil temperature at engine restart. Even if it exists, the holding | maintenance control amount after restart can be calculated suitably, considering the change of the oil temperature. Therefore, the valve timing control at the time of engine restart can be appropriately performed.

  In addition, it is considered that the temperature characteristic of the holding control amount may be expressed by a complicated function consisting of a plurality of variables. However, with the above configuration, the engine can be stopped without providing a plurality of learning areas for learning. Oil temperature change from start to restart can be predicted. Therefore, it is also preferable in that the valve timing control at the time of engine restart can be properly performed while suppressing the learning process from becoming complicated.

  Specifically, as in the invention described in claim 2, the post-restart holding control amount is calculated so that the amount of change from the learned value becomes larger as the engine stop time is longer. This is because as the engine stop time is longer, the oil temperature decreases from the learning time point before the engine stop, and the amount of change in the hold control amount increases.

  When the engine stop time is relatively short, the change in the oil temperature from the engine stop to the engine restart is small, and it is considered that the appropriate value of the hold control amount at the time of engine restart is not so different from that before the engine stop. On the other hand, when the engine stop time becomes longer, the accuracy of predicting the oil temperature change due to the engine stop time is lowered, and when the hold control amount is calculated based on the engine stop time, the deviation from the actual value is likely to increase.

  Therefore, in the invention according to claim 3, the post-restart holding control amount is calculated based on a comparison result between the engine stop time and a determination value, and the learning value is used as the determination value. It includes a first elapsed time that defines a period for the post-retention control amount and a second elapsed time that defines a period for which the learned value corrected according to the engine stop time is the post-restart retention control amount. When the engine stop time is equal to or shorter than the first elapsed time, the learning value is set as the post-restart holding control amount, and when the engine stop time is greater than the first elapsed time and equal to or shorter than the second elapsed time, the engine stop time is determined. The learning value corrected according to the above is used as the holding control amount after restart, and the holding control amount after restart is not calculated using the learning value when the learning value is larger than the second elapsed time. As a result, the post-restart holding control amount can be appropriately set according to the engine restart situation.

  The change in oil temperature of the hydraulic pressure regulator during the period from engine stop to restart differs according to the oil temperature when the engine is stopped. Specifically, the higher the oil temperature when the engine is stopped, the lower the oil temperature is. It is conceivable that the amount of change (decrease rate) increases. Therefore, as in the invention described in claim 4, the oil temperature detecting means for detecting the oil temperature of the hydraulic pressure adjusting device when the engine is stopped is provided, and the restart is performed based on the oil temperature detected by the oil temperature detecting means. The post-holding control amount may be corrected. By doing so, it is possible to improve the calculation accuracy of the holding control amount when the engine is restarted.

  Also, the oil temperature change during the period from engine stop to restart is different depending on the outside air temperature. Specifically, it is considered that the lower the outside air temperature during the stop period, the greater the oil temperature decrease rate. . Accordingly, as in the invention described in claim 6, an outside air temperature detecting means for detecting the outside air temperature is provided, and the post-restart holding control amount is corrected based on the outside air temperature detected by the outside air temperature detecting means. In addition, the calculation accuracy of the holding control amount at the time of engine restart can be improved.

1 is an overall schematic configuration diagram of a valve timing control system. The figure which shows the relationship between a control duty value and camshaft advance angular velocity. The figure which shows an example of the temperature characteristic of a holding | maintenance duty value. The flowchart which shows the process sequence of a holding | maintenance point learning process. The figure which shows an example of a stop time correction | amendment calculation map. The time chart which shows the specific aspect of a holding | maintenance point learning process. The figure which shows the stop time correction | amendment calculation map in other embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. In the present embodiment, a valve timing control system is constructed for an intake valve of an engine that is an internal combustion engine. In the control system, valve timing control is performed with an electronic control unit (hereinafter referred to as ECU) as a center. An overall schematic configuration diagram of this control system is shown in FIG.

  In the engine 11, a crankshaft 12 that is an output shaft of the engine 11 is connected to a sprocket 14 of the intake camshaft 16 and a sprocket 15 of the exhaust camshaft 17 via a timing chain (or timing belt) 13. When the crankshaft 12 is rotated by driving the engine 11, the rotational driving force is transmitted to the intake camshaft 16 and the exhaust camshaft 17. Open and close.

  The intake valve is provided with a variable valve timing device 18. In the present embodiment, the variable valve timing device 18 is hydraulically driven, and the rotation phase (cam shaft phase) of the intake cam shaft 16 with respect to the crankshaft 12 is changed by this device 18 so that the intake valve opening / closing timing ( Valve timing) is changed.

  Specifically, the variable valve timing device 18 includes a housing 22 in which a plurality of hydraulic chambers 21 are formed. The housing 22 is fixed to the sprocket 14 of the intake camshaft 16. A vane 24 formed on the outer periphery of the rotor 23 is disposed in the hydraulic chamber 21, and the hydraulic chamber 21 is partitioned into an advance chamber 25 and a retard chamber 26 by the vane 24.

  A hydraulic pump 28 is connected to the advance chamber 25 and the retard chamber 26 via a hydraulic circuit 27. The hydraulic pump 28 uses the engine 11 as a drive source, and is driven by transmitting power from the crankshaft 12 via a timing chain. Accordingly, when the crankshaft 12 rotates and the hydraulic pump 28 is driven, the oil in the oil pan 29 can be supplied to the advance chamber 25 and the retard chamber 26 as hydraulic oil.

  In the hydraulic circuit 27, an oil control valve (OCV) 31 is disposed at an intermediate position between the hydraulic pump 28 and the advance chamber 25 and the retard chamber 26. The OCV 31 is a four-port three-position switching valve that drives the valve body by a solenoid 32 and a spring 33, and the position of the valve body is set to an advance supply position for supplying hydraulic oil to the advance chamber 25 and to the retard chamber 26. It is possible to switch between a retard supply position that supplies hydraulic oil and a holding position that does not supply hydraulic oil to either the advance chamber 25 or the retard chamber 26. In the OCV 31, the amount of hydraulic oil supplied from the oil pan 29 to the advance chamber 25 and the retard chamber 26 is adjusted by switching control of the valve body position. By adjusting the hydraulic oil amount, the rotational direction and rotational amount of the rotor 23 (vane 24) with respect to the housing 22 are adjusted according to the hydraulic oil amount, and the rotational phase of the intake cam shaft 16 with respect to the crankshaft 12 (cam shaft phase). ) Is changed.

  In the present embodiment, the variable valve timing device 18 is provided in the intake valve, but the variable valve timing device may be provided in both the exhaust valve or both the intake valve and the exhaust valve.

  In addition, this system is provided with a cam angle sensor 34 that outputs a cam angle signal for each predetermined cam angle at a position facing the intake camshaft 16, and at a position facing the crankshaft 12. A crank angle sensor 35 that outputs a crank angle signal for each crank angle is provided. Furthermore, this system is provided with an oil temperature sensor 36 that detects the temperature of the hydraulic oil of the OCV 31, an IG switch 37 that can be switched based on the operation of the driver, and the like.

  The ECU 40 is an electronic control device including a known microcomputer and the like, and based on detection results of various sensors provided in the present system, fuel injection amount control, ignition control, idle stop control, valve timing control. Implement various engine controls.

  In general, the idle stop control automatically stops the engine 11 when a predetermined ISS stop condition is satisfied during the idling operation of the engine 11, and thereafter, when the predetermined ISS restart condition is satisfied, there is an engine restart request. The engine 11 is restarted. The ISS stop condition includes, for example, at least one of the fact that the accelerator operation amount has become zero, that the brake pedal has been depressed, the vehicle speed has decreased to a predetermined value, or the like. Further, the ISS restart condition includes at least one of an accelerator operation performed when the engine is stopped, a brake pedal being released, and the like.

  For details on the valve timing control, the ECU 40 calculates the rotational phase (actual cam shaft phase) of the cam shaft 16 with respect to the crank shaft 12 based on the output signals of the cam angle sensor 34 and the crank angle sensor 35, for example. A target camshaft phase is calculated according to engine operating conditions. Then, in order to make the actual cam shaft phase (actual valve timing) coincide with the target cam shaft phase (target valve timing), the control duty value of the solenoid 32 of the OCV 31 is calculated, and the solenoid 32 is energized and controlled by the control duty value.

  In the energization control of the solenoid 32, in this embodiment, the energization control is performed based on the feedback control amount corresponding to the deviation between the target cam shaft phase and the actual cam shaft phase and the holding duty value. This holding duty value is a duty value required to place the valve body in the holding position, in other words, a duty value for holding the camshaft phase at the current position.

  Specifically, when the valve opening timing of the intake valve is changed to the advance side, the control duty value is set to a value Dad (for example, 70%) larger than the holding duty value Dnt, and the valve body of the OCV 31 is set to the advance supply position. In the case of changing to the retard side, the control duty value is set to a value Dla (for example, 0%) smaller than the holding duty value Dnt, and the valve body of the OCV 31 is set to the retard supply position. As a result, the intake camshaft 16 is rotated relative to the crankshaft 12 toward the advance side or the retard side, and the valve opening timing of the intake valve is changed to the advance side or the retard side.

  Also, when the valve opening timing of the intake valve reaches a desired position, the valve duty of the OCV 31 is maintained at the holding position by setting the control duty value to the holding duty value Dnt (for example, 40%), and the crankshaft 12, the relative rotational position of the intake camshaft 16 with respect to 12 is held at the current position. Thereby, the valve opening timing of the intake valve is maintained at the current timing.

  FIG. 2 shows the relationship between the control duty value of the solenoid 32 and the actual valve timing changing speed (cam shaft advance speed). In FIG. 2, the camshaft rotational speed when the valve timing is changed to the advance side is shown as a positive value, and the camshaft rotational speed when the valve timing is changed to the retard side is shown as a negative value.

  In FIG. 2, the control duty value at the point A at which the camshaft advance angular velocity becomes zero corresponds to the holding duty value Dnt. The valve timing is changed to the advance side when the control duty value is larger than the holding duty value Dnt, and the valve timing is delayed when the control duty value is smaller than the holding duty value Dnt. It is changed to the corner side.

  This holding duty value varies depending on the tolerance of the OCV 31, the temperature of the hydraulic oil, a change with time, and the like, and particularly has a high temperature dependency and is likely to vary due to the influence of the temperature of the hydraulic oil.

  FIG. 3 is a diagram illustrating an example of a temperature characteristic of the holding duty value dutykep. In FIG. 3, the holding duty value dutykep becomes minimum at the intermediate temperature tmpmid (becomes a value on the retard side), and becomes larger (becomes a value on the advance side) as the temperature becomes lower or higher than the intermediate temperature tmpmid. In FIG. 3, the intermediate temperature tmpmid is at or near the warm-up completion temperature of the engine 11, specifically, for example, 90 ° C.

  In view of the fact that the holding duty value of the OCV 31 varies due to various factors, the ECU 40 performs learning of the holding duty value (holding point learning) for the OCV 31 as a target. Specifically, for example, during engine operation, the learning value obtained by holding point learning (holding point learned value dutylrn) is used as a holding duty value, and the OCV 31 is controlled using this value as a target value for the actual camshaft phase. Duty value is calculated.

For details on holding point value learning,
The engine rotational speed is larger than a judgment value (for example, 500 rpm) The absolute value of the deviation between the target cam shaft phase and the actual cam shaft phase is smaller than the judgment value (substantially zero), and the state is a predetermined time When the two conditions are satisfied, the holding point learning value dutylrn (i) is calculated by the following equation (1). Then, the calculated holding point learning value dutylrn (i) is stored as a current learning value in a backup memory such as an EEPROM or a backup RAM and updated.
dutylrn (i) = dutyrnrn (i-1) + dutyfb × β (1)
Here, dutyfb is the deviation between the target camshaft phase and the actual camshaft phase, and β is the feedback gain.

  By the way, when the engine 11 is stopped and then the engine 11 is restarted in response to the restart request, since the holding point learning execution condition is not satisfied in the predetermined period after the restart request, the current engine An optimal holding duty value for the operating state cannot be acquired by executing holding point learning. Therefore, when the engine is restarted, for example, it is conceivable to use the learned value dutylrn acquired before the engine is stopped as the current holding duty value.

  However, when the engine 11 is restarted, it is conceivable that the temperature of the hydraulic oil decreases during the engine stop period from the engine stop to the restart request. Therefore, in the valve timing control at the time of engine restart, when the holding point learning value dutylrn learned before engine stop is used as the current holding duty value, depending on the engine stop time, the holding duty value is not appropriate. The valve timing control may not be properly performed.

  Therefore, in the present embodiment, the engine stop time from the engine stop (rotation stop timing of the crankshaft 12) to the engine restart request is measured, and based on the measured engine stop time and the learning value of the holding duty value, A post-restart holding duty value is calculated as a holding duty value used in a period after the engine restart request and until the holding point learning execution condition is satisfied. Then, using the calculated post-restart holding duty value, valve timing control is performed for a period until the holding point learning is started.

  FIG. 4 is a flowchart showing a processing procedure of holding point learning processing of the present system. This process is repeatedly executed by the ECU 40 at predetermined intervals.

In FIG. 4, first, in step S11, it is determined whether or not the engine has been started. Here, it is determined that the engine has been started when the engine speed NE is greater than a determination value η (for example, 500 rpm). If the engine has been started, the process proceeds to step S12, where the absolute value absd of the deviation between the target cam shaft phase and the actual cam shaft phase is smaller than the determination value α (predetermined value near zero) and the state (absd <α). It is determined whether or not has continued for a predetermined time. When an affirmative determination is made in step S12, the process proceeds to step S13, and a provisional learning value dutylrnb (i) is calculated by the following equation (2).
dutylrnb (i) = dutyrnrn (i-1) + dutyfb × β (2)

  Thereafter, in step S14, the provisional learning value dutylrnb (i) is limited by the upper limit guard value dutymax and the lower limit guard value dutymin, and the value after the guard process is set as the current holding point learning value dutylrn (i). In the present embodiment, the upper guard value dutymax is set to, for example, a duty value of 70%, and the lower limit guard value dutymin is set to, for example, a duty value of 30%.

  On the other hand, in the case before the engine is started, for example, after the engine restart request associated with the establishment of the ISS restart condition and before the engine speed reaches the determination value η, the process proceeds to step S15 and the engine is stopped. It is determined whether or not the time from the engine to the engine restart request (engine stop time) is equal to or shorter than the allowable determination time T1.

  Regarding the engine stop time In this embodiment, the ECU 40 has a built-in soak timer. With this soak timer, the time from when the engine speed NE becomes zero (from the rotation stop timing of the crankshaft 12) to the engine restart request is calculated. It is measured and stored in a backup memory or the like each time. In step S15, the stored engine stop time is read, and the read engine stop time is compared with the allowable determination time T1. In this embodiment, the allowable determination time T1 is determined in advance as a time during which the hydraulic oil temperature (oil temperature at the time of stop) can be maintained at the rotation stop timing (NE = 0 timing) of the crankshaft 12 in the engine stop state. .

  If the engine stop time is less than or equal to the allowable determination time T1, the process proceeds to step S16, where the previous learned value dutylrn (i-1), that is, the last learned value before engine stop, is set as the provisional learning value dutyrnrnb (i). In step S14, a guard process is performed on the provisional learning value dutyrnrnb (i) using the upper guard value dutymax and the lower guard value dutymin.

  On the other hand, if the engine stop time exceeds the allowable determination time T1, the process proceeds to step S17 to determine whether or not the engine stop time is equal to or less than the invalid determination time T2. The invalidity determination time T2 is a value larger than the allowable determination time T1, and is determined based on, for example, a time during which the engine stop state is allowed to be continued by the idle stop control (ISS stop permission time). In the present embodiment, the invalidity determination time T2 is set as the ISS stop allowable time.

If the engine stop time is equal to or shorter than the invalidity determination time T2, the process proceeds to step S18, where the provisional learning value dutylrnb (i) is calculated by the following equation (3). The guard process is performed to obtain the current holding point learning value dutylrn (i).
dutylrnb (i) = (dutylrn (i-1) -dutymin) × δ + dutymin (3)
Here, δ is a correction coefficient indicating the ratio of how much the previous learning value dutylrn (i-1) is reflected in the current learning value (temporary learning value dutylrnb (i)), and is set according to the engine stop time Is the value to be

  FIG. 5 is an example of a stop time correction calculation map used for calculating the correction coefficient δ. FIG. 5 defines the case where the oil temperature when the engine is stopped is an appropriate temperature, specifically, the case where the oil temperature is an intermediate temperature tmpmid (engine warm-up completion temperature). In FIG. 5, the correction coefficient δ is determined based on the temperature characteristic of FIG. 3 that the holding duty value dutykep increases toward the lower temperature side with respect to the intermediate temperature tmpmid. Specifically, the engine stop time is “0”. The correction coefficient δ = 1, and in the range from the engine stop time “0” to the invalidity determination time T2, the correction coefficient δ larger than “1” is set as the engine stop time becomes longer. That is, according to this map, as the engine stop time is longer, a value larger than the previous learning value dutyrnrn (i-1) is set as the temporary learning value dutyrnrnb (i).

  Returning to the description of FIG. 4, when the engine stop time exceeds the invalidity determination time T2, the process proceeds to step S19. In step S19, the lower limit guard value dutymin is set to the holding point learning value dutylrn (i), and this process ends. Therefore, for example, when the engine is started when the IG switch 37 is switched from OFF to ON, and the engine stop time from the engine stop immediately before that to the current engine start request (IG ON) exceeds the invalidity determination time T2. In step S19, the lower limit guard value dutymin is set as the hold point learning value dutyrnrn (i). That is, if the engine stop time becomes long, it is considered that the change in the oil temperature from the engine stop time may not be accurately grasped depending on the engine stop time. Therefore, in this embodiment, the invalidity determination time T2 is set, and when the invalidity determination time T2 is exceeded, the holding point learning value is not calculated based on the engine stop time, and the lower limit guard value is set as a safer value. Set dutymin.

  In the present embodiment, if the engine stop time when the IG switch 37 is switched from OFF to ON is relatively short and is shorter than the invalidity determination time T2, in step S18, the previous learned value dutyrnrn (i− Based on 1) and the engine stop time, the hold point learning value dutylrn (i) is calculated.

  FIG. 6 is a time chart showing a specific mode of the holding point learning process of the present system. In the figure, (a) shows a case where there is an engine restart request within the allowable determination time T1 from the rotation stop timing of the crankshaft 12, and (b) is after the elapse of the allowable determination time T1 from the rotation stop timing. This shows a case where there is an engine restart request at a timing before the invalidity determination time T2. In FIG. 6, it is assumed that engine stop / restart is performed by idle stop control.

  In FIG. 6A, it is assumed that the ISS stop condition is satisfied at timing t11 and the rotation of the crankshaft 12 is stopped at timing t12. At this time, when the ISS restart condition is satisfied at the timing t13 within the allowable determination time T1 from the rotation stop timing t12 (when the restart is requested), the restart that is the holding duty value Dutykep at the time of engine restart As the post-holding duty value (A ′ in the figure), a learning value dutyrnrn (A in the figure) that is stored and updated by the last learning before the engine is stopped is set.

  Further, in FIG. 6B, after the ISS stop condition is satisfied at timing t21 and the rotation of the crankshaft 12 is stopped at timing t22, the invalidity determination time after the allowable determination time T1 has elapsed from the rotation stop timing t22. When the ISS restart condition is satisfied at timing t23 within T2 (when a restart request is made), the retention duty value after restart (A 'in the figure) is stored by the last learning before the engine is stopped. A value calculated based on the updated learning value dutylrn (A in the figure) and the engine stop time is set. In the present embodiment, a duty value that is larger than the learned value dutylrn is set as the post-restart holding duty value.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  Based on the engine stop time from the engine stop to the engine restart request and the hold point learning value dutylrn learned before the engine stop until the execution condition for holding point learning is satisfied after the engine restart request Since the holding duty value (holding duty value after restart) used in the period of time is calculated, the oil temperature of the OCV 31 decreases while the engine is stopped, and the oil temperature at the time of learning and the oil temperature at the time of engine restart are shifted. Even when this occurs, the post-restart holding duty value can be calculated while taking into account the change in the oil temperature. Therefore, the valve timing control at the time of engine restart can be appropriately performed.

  In addition, by adopting the above-described configuration, it is possible to suitably predict the oil temperature change from the engine stop to the restart without providing a plurality of learning areas during learning. Therefore, even when the temperature characteristic of the holding duty value is a complicated function as shown in FIG. 2, it is preferable to change the oil temperature from the engine stop to the restart while avoiding complicated learning processing. As a result, the valve timing control when the engine is restarted can be appropriately performed.

  When the engine stop time is less than or equal to the allowable determination time T1, the holding point learned value dutylrn is used as the hold duty value after restart. When the engine stop time exceeds the allowable determination time T1 and is less than or equal to the invalid determination time T2, the engine stop time depends on the engine stop time. Since the hold point learning value dutylrn corrected in this way is used as the hold duty value after restart, during the period in which there is a difference between the oil temperature at the time of learning and the oil temperature at the time of engine restart, it The holding duty value corresponding to the oil temperature at the start can be obtained.

  When the engine stop time becomes longer, the prediction accuracy of the oil temperature change due to the engine stop time decreases, and when the hold control amount is calculated based on the engine stop time, the deviation from the actual value is likely to increase. When the stop time exceeds the invalidity determination time T2, since the holding point learning value dutylrn is not used in calculating the post-restart holding duty value, it is possible to suppress a reduction in the calculation accuracy of the post-restarting holding duty value. it can. In particular, when the engine stop time exceeds the invalidity determination time T2, the post-restart hold duty value is set to the lower limit duty value dutymin, so that the occurrence of misfire can be suppressed.

(Other embodiments)
This invention is not limited to said content, For example, you may implement as follows.

  The oil temperature of the OCV 31 when the engine is stopped is detected, and the post-restart holding duty value is corrected based on the oil temperature. The oil temperature change during the period from engine stop to engine restart differs depending on the oil temperature when the engine is stopped. Specifically, the higher the oil temperature when the engine is stopped, the higher the oil temperature change rate during the engine stop period. (Decrease rate) is considered to increase. Therefore, when calculating the post-restart holding duty value, the relationship between the oil temperature change amount and the engine stop time can be made more accurate by taking into account the oil temperature when the engine is stopped. The calculation accuracy of the holding duty value can be further increased.

  Specifically, for example, the oil temperature sensor 36 detects the oil temperature of the OCV 31 at the timing of stopping the rotation of the crankshaft 12 (oil temperature at the time of stop). Then, the correction coefficient δ calculated based on the map shown in FIG. 5 is multiplied or added by a coefficient corresponding to the stop oil temperature, thereby correcting the correction coefficient δ to a value corresponding to the stop oil temperature. At this time, for example, the correction coefficient δ is set to a larger value as the oil temperature during stoppage is higher.

  Further, instead of using a coefficient corresponding to the oil temperature at the time of stop, a plurality of stop time correction calculation maps are stored according to the oil temperature at the time of stop, and the oil temperature at the time of stop detected by the oil temperature sensor 36 is used. On the basis of this, a configuration may be adopted in which any one of the plurality of stored calculation maps is selected, and the post-restart holding duty value is calculated based on the selected calculation map.

  -It is set as the structure provided with the external air temperature detection means (for example, external air temperature sensor) which detects external air temperature, and correct | amends the holding duty value after a restart based on the external air temperature detected by the external air temperature detection means. This is because the change in the oil temperature during the period from the engine stop to the engine restart differs depending on the outside air temperature, and the lower the outside air temperature, the greater the change rate (decrease rate) of the oil temperature during the engine stop period.

  Specifically, for example, the correction coefficient δ calculated based on the map of FIG. 5 is multiplied or added by a coefficient corresponding to the outside air temperature, thereby correcting the correction coefficient δ to a value corresponding to the outside air temperature. . At this time, for example, the correction coefficient δ is set to a larger value as the outside air temperature is lower. Alternatively, a plurality of stop time correction calculation maps are stored according to the outside air temperature, and a post-restart holding duty value is calculated based on a calculation map selected based on the outside air temperature from the stored plurality of calculation maps. Also good.

  The outside air temperature may be detected when the engine is stopped (for example, rotation stop timing of the crankshaft 12), or may be detected when the engine is restarted. Further, in consideration of the difference between the outside air temperature when the engine is stopped and the outside air temperature when the engine restart is requested, the correction coefficient δ may be increased or decreased as the difference increases.

  In the above embodiment, as shown in FIG. 3, the temperature characteristic of the holding duty value is such that the holding duty value dutykep is minimum at the intermediate temperature tmpmid, and the holding duty value increases toward the low temperature side or the high temperature side with respect to the intermediate temperature tmpmid. Although the description has been made on the assumption that the dutykep is increased, the present invention may be applied to a configuration showing temperature characteristics different from those in FIG. Specifically, for example, the present invention is applied to a configuration showing a characteristic that the holding duty value dutykep increases as the oil temperature increases or a configuration that shows a characteristic that the holding duty value dutykep decreases as the oil temperature increases. In this case, a stop time correction calculation map (see FIG. 5) is set in consideration of the temperature characteristics. For example, when the temperature characteristic indicates that the holding duty value dutykep increases as the oil temperature increases, the stop time correction calculation map has a correction coefficient δ = 1 when the engine stop time is “0”, for example, as shown in FIG. In the range from the engine stop time “0” to the invalidity determination time T2, the correction coefficient δ smaller than “1” is set as the engine stop time becomes longer.

  3 instead of the stop time correction calculation map of FIG. 5, the holding duty value dutykep is minimum at the intermediate temperature tmpmid, and the holding duty value dutykep increases as the intermediate temperature tmpmid becomes lower or higher temperature side. The stop time correction calculation map set based on the characteristics is used.

  In the case of engine stop / restart by the idle stop control, the post-restart holding duty value is calculated based on the engine stop time and the learned value, and the engine stop time in the case of engine stop / start accompanying switching of the IG switch 37 The retention duty value after restart is calculated without using. In this case, at the time of engine start accompanying switching of the IG switch 37, for example, the lower limit guard value dutymin is used as the hold duty value after restart regardless of the elapsed time from the previous engine stop.

  When the IG switch 37 is switched from on to off, the holding point learning value dutylrn (i) stored in the memory or the like is deleted. In this case, when the IG switch 37 is switched from OFF to ON next time, for example, the valve timing control is performed with the holding point learning value dutylrn (i) at the start of the engine as an initial value (for example, the lower limit guard value dutymin).

  DESCRIPTION OF SYMBOLS 11 ... Engine, 16 ... Intake cam shaft, 17 ... Exhaust cam shaft, 18 ... Variable valve timing apparatus (variable valve mechanism), 25 ... Advance chamber, 26 ... Delay chamber, 28 ... Hydraulic pump, 31 ... Oil control valve (Hydraulic pressure adjusting device), 40... ECU.

Claims (5)

A variable valve mechanism that adjusts the valve timing on the intake side or the exhaust side of the engine using hydraulic pressure as a drive source, and a hydraulic pressure adjustment device that adjusts the hydraulic pressure that drives the variable valve mechanism, in response to a restart request after the engine stops Applies to the engine to be restarted,
The control amount of the hydraulic pressure adjusting device is calculated based on a feedback control amount corresponding to a deviation between the target valve timing and the actual valve timing and a holding control amount for maintaining the current valve timing, and based on the control amount Variable valve timing control that drives the variable valve mechanism by adjusting the hydraulic pressure by the hydraulic pressure adjusting device and that learns the holding control amount on condition that a predetermined execution condition is satisfied during operation of the engine In the device
Measuring means for measuring the engine stop time from the engine stop to the restart request;
Based on the engine stop time measured by the measuring means and the learned value of the holding control amount, holding after restart which is a holding control amount used after the restart request until the execution condition is satisfied Control amount calculation means for calculating the control amount;
A variable valve timing control device comprising:   2. The variable valve timing control device according to claim 1, wherein the control amount calculation unit calculates the post-restart holding control amount so that the amount of change from the learned value becomes larger as the engine stop time is longer. . The control amount calculation means includes
Based on the comparison result between the engine stop time and the determination value, the post-restart holding control amount is calculated,
As the determination value, a first elapsed time that defines a period in which the learning value is the holding control amount after restart, and a period in which the learning value corrected according to the engine stop time is the holding control amount after restart. Including the second elapsed time
When the engine stop time is equal to or less than the first elapsed time, the learning value is set as the post-restart holding control amount, and when the engine stop time is greater than the first elapsed time and equal to or less than the second elapsed time, 3. The post-restart holding control amount is not calculated using the learning value when the learning value corrected in this way is used as the post-restart holding control amount and is greater than the second elapsed time. Variable valve timing control device. An oil temperature detecting means for detecting the oil temperature of the hydraulic pressure adjusting device when the engine is stopped;
4. The variable valve timing control device according to claim 1, wherein the control amount calculation unit corrects the post-restart holding control amount based on the oil temperature detected by the oil temperature detection unit. 5. An outside air temperature detecting means for detecting the outside air temperature,
5. The variable valve timing control device according to claim 1, wherein the control amount calculating unit corrects the post-restart holding control amount based on an outside air temperature detected by the outside air temperature detecting unit.

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