WO2008142516A1

WO2008142516A1 - Control apparatus and control method for valve operating system

Info

Publication number: WO2008142516A1
Application number: PCT/IB2008/001212
Authority: WO
Inventors: Seiko Tamada
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2007-05-16
Filing date: 2008-05-15
Publication date: 2008-11-27
Also published as: JP2008286053A

Abstract

A control apparatus for a valve operating system having a control shaft driven within a movable range between a first end and a second end, an actuator that drives the control shaft to change a valve characteristic of an internal combustion engine, a control portion that calculates an absolute position of the control shaft on the basis of a reference position and an amount of displacement from the reference position, a learning portion that displaces the control shaft to one of the first end and the second end of the movable range to learn the absolute position of the control shaft when a predetermined learning condition is fulfilled during the execution of fuel cut control in the internal combustion engine, and a learned value updating portion mat updates the absolute position during the execution of fuel cut control in the internal combustion engine when the absolute position is learned.

Description

CONTROLAPPARATUS AND CONTROL METHOD FOR VALVE OPERATING

SYSTEM

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a control apparatus and a control method that are applied to a valve operating system having a control shaft driven within a movable range and an actuator for driving the control shaft to change the valve characteristic of an internal combustion engine through the driving of the control shaft by the actuator, and that calculate an absolute position of the control shaft on the basis of a reference position and an amount of displacement of the control shaft from the reference position. 2. Description of the Related Art

There is a valve operating system described in, for example, Japanese Patent Application Publication No. 2003-41977 (JP-A-2003-41977) as a mechanism for changing the valve characteristic of intake valves of an internal combustion engine in accordance with the operational state of the engine. This valve operating system changes the maximum lift amount of the valves of the engine by driving a cam shaft (control shaft) provided with three-dimensional cams, whose noses change in height in an axial direction, by means of an actuator in the axial direction. Accordingly, in this valve operating system, the accurate control of the position of the cam shaft is important in making the maximum lift amount suited for the operational state of the engine.

Although various methods have been proposed to detect the position of the cam shaft (control shaft), there is, for example, a method in which the valve operating system is provided with a sensor for detecting the position of the cam shaft so that the position of the cam shaft, that is, the maximum lift amount of the intake valves is detected on the basis of the output of the sensor. In this method, however, due to the dispersion of the initial position where the sensor is mounted, the dispersion of the output of the sensor provided for each valve operating system, or changes in sensor characteristic resulting from changes in temperature or the like, there is a discrepancy between the position of the cam shaft calculated on the basis of the detected output of the sensor and the actual position of the cam shaft. As a result, the position of the cam shaft cannot be accurately detected.

With this background, in a control apparatus for a valve operating system described in Japanese Patent Application Publication No. 2002-349215 (JP-A-2002-349215), a predetermined reference position of a control shaft, within a movable range restricted by a stopper, is stored, and an amount of displacement of the control shaft from this stored reference position is detected by a sensor. An absolute position of the control shaft is then calculated on the basis of this amount of displacement and the reference position, and an actuator is controlled such that the absolute position of the control shaft coincides with a target position. In this apparatus, the control shaft is displaced to an end of the movable range when a predetermined learning condition is fulfilled, the absolute position of the control shaft is learned when it is determined that the control shaft has reached the end of the movable range, and the position of the control shaft calculated at that time is updated to the learned absolute position. Thus, even when there is a discrepancy between the calculated position of the control shaft and the actual position thereof as a result of, for example, changes in the characteristic of the sensor or the like, the calculated position of the control shaft can be made to coincide with the actual position thereof.

In the case where the learning of absolute position is carried out, a previously obtained absolute position is updated to a new absolute position. The absolute position of the control shaft corresponds to a valve characteristic such as the maximum lift amount of the intake valves or the like. Therefore, a sudden change in the absolute position leads to a sudden change in the valve characteristic. In the event of a sudden change in the valve characteristic, a sudden change in fuel injection amount or air-fuel ratio, which is controlled on the basis of the valve characteristic, may be caused. Thus, in the case where the learning of absolute position is carried out, a previously obtained absolute position is gradually updated to a new absolute position.

However, when the absolute position obtained prior to the learning is different from the actual position, there is an inadequate relationship between the absolute position and a control value corresponding thereto. It is therefore desirable to update the absolute position swiftly,

SUMMARY OF THE INVENTION

The invention provides a control apparatus and a control method for a valve operating system that carry out the updating of absolute position while suppressing the influence of a sudden change in valve characteristic.

A first aspect of the invention relates to a control apparatus for a valve operating system having a control shaft driven within a movable range between a first end and a second end, and an actuator that drives the control shaft to change a valve characteristic of an internal combustion engine. This control apparatus is equipped with a control portion that calculates an absolute position of the control shaft on the basis of a reference position and an amount of displacement of the control shaft from the reference position, a learning portion that displaces the control shaft to one of the ends of the movable range to learn an absolute position of the control shaft, when a predetermined learning condition is fulfilled during the execution of fuel cut control in the internal combustion engine, and a learned value updating portion that updates the absolute position during the execution of the fuel cut control in the internal combustion engine when the absolute position is learned by the learning portion.

According to the foregoing construction, when the predetermined learning condition is fulfilled during the execution of fuel cut control in the internal combustion engine, the control shaft is displaced to one of the ends of the movable range to learn the absolute position thereof. Therefore, the amount of fuel injection can be prevented from changing in displacing the control shaft to one of the ends of the movable range. The absolute position is then updated during the execution of fuel cut control in the internal combustion engine, when the absolute position is learned by the learning portion. Therefore, even when the absolute position of the control shaft changes in accordance with the updating thereof, the amount of fuel injection can be prevented from changing. As a result, the relationship between valve characteristic and fuel injection amount can be restrained from changing. Therefore, the absolute position can be swiftly updated while suppressing the influence of a sudden change in valve characteristic.

In the foregoing aspect of the invention, the learned value updating portion may immediatelyupdate the absolute position when the absolute position is learned by the learning portion during the execution of fuel cut control in the internal combustion engine. For example, in the case where the absolute position is gradually updated, if the cutting of fuel supply is suspended before the updating of the absolute position is completed, the updating of the absolute position is continued after the cutting of fuel supply is suspended. Thus, the relationship between valve characteristic and fuel injection amount may remain inadequate. In this respect, according to the foregoing construction, the absolute position is immediately updated when the reference position is learned by the learning portion during the cutting of fuel supply in the engine. Therefore, the absolute position can be updated rather swiftly. Therefore, in comparison with the case where, for example, the absolute position is gradually updated, the relationship between valve characteristic and fuel injection amount can be restrained from remaining inadequate as a result of the suspension of the cutting of fuel supply before the completion of the updating of the absolute position.

A second aspect of the invention relates to a control method for a valve operating system having a control shaft driven within a movable range between a first end and a second end, and an actuator that drives the control shaft to change a valve characteristic of an internal combustion engine. This control method includes calculating an absolute position of the control shaft on the basis of a reference position and an amount of displacement of the control shaft from the reference position, displacing the control shaft to one of the first end and the second end to learn the absolute position of the control shaft when a predetermined learning condition is fulfilled during the execution of fuel cut control in the internal combustion engine, and updating the absolute position during the execution of the fuel cut control in the internal combustion engine when the absolute position of the control shaft is learned.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and further objects, features and advantages of the invention will become apparent from the following description of an example embodiment with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein: FIG. 1 is a view showing a cross-sectional structure of part of a valve operating system of an internal combustion engine according to one embodiment of the invention;

FIG. 2 is a plan view showing a mode of arrangement of the valve operating system of the internal combustion engine according to the embodiment of the invention;

FIG. 3 is a cutaway perspective view showing an internal structure of an intermediary drive mechanism according to the embodiment of the invention;

FIG 4 is a block diagram showing a control shaft, a brushless motor, and a microcomputer according to the embodiment of the invention;

FIGS. 5 A to 5H are timing charts showing patterns of changes in output waveforms of respective sensors according to the embodiment of the invention and count values of respective counters according to the embodiment of the invention;

FIGS. 6 A .and 6B are views showing relationships among output signals of the respective sensors, an electric angle count, and a position count according to the embodiment of the invention;

FIG. 7 is a flowchart showing a processing procedure of Lo end learning carried out by a control apparatus according to the embodiment of the invention; and

FIG. 8 is composed of timing charts for explaining one concrete example of Lo end learning carried out by the control apparatus according to the embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENT Hereinafter, a control apparatus for a valve operating system of an internal combustion engine mounted on a vehicle according to one embodiment of the invention will be described with reference to FIGS. 1 to 8. FIG. 1 is a view showing a cross-sectional structure of part of the valve operating system of the internal combustion engine mounted on the vehicle. FIG. 2 is a plan view showing a mode of arrangement of the valve operating system of the internal combustion engine.

As shown in FIGS. 1 and 2, the internal combustion engine has four cylinders (only one of which is shown in FIG. 1), and a cylinder head 2 of the internal combustion engine is provided in a reciprocable manner with pairs of exhaust valves 10 and pairs of intake valves 20 corresponding to these cylinders respectively. The cylinder head 2 is also provided with exhaust valve opening/closing devices 90 and intake valve opening/closing devices 100 corresponding to the exhaust valves 10 and the intake valves 20 respectively.

Each of the exhaust valve opening/closing devices 90 is provided with a corresponding one of lash adjusters 12 corresponding to a corresponding one of the exhaust valves 10. Each of rocker arms 13 is bridged between a corresponding one of the lash adjusters 12 and a corresponding one of the exhaust valves 10. Each of the rocker arms 13 is supported at a base end thereof by a corresponding one of the lash adjusters 12, and abuts at a tip thereof on a base end portion of a corresponding one of the exhaust valves 10. An exhaust cam shaft 14 is rotatably supported by the cylinder head 2. This exhaust cam shaft 14 is rotated in a manner interlocking with rotation of an output shaft of the engine. A plurality of cams 15 are formed on the exhaust cam shaft 14, and each of rollers 13a provided on intermediate regions of the rocker arms 13 abuts on an outer peripheral face of a corresponding one of the cams 15. Each of the exhaust valves 10 is provided with a corresponding one of retainers 16, and each of valve springs 11 is provided between a corresponding one of the retainers 16 and the cylinder head 2. Due to an urging force of each of the valve springs 11, a corresponding one of the exhaust valves 11 is urged in its valve closing direction. Thus, each of the rollers 13a of the rocker arms 13 is pressed against the outer peripheral face of a corresponding one of the cams 15. When the cams 15 rotate during operation of the engine, each of the rocker arms 13 rocks around its region supported by a corresponding one of the lash adjusters 12. As a result, each of the exhaust valves 10 is driven by a corresponding one of the rocker arms 13 to be opened/closed. As the opening degree of each of the exhaust valves 10, namely, the lift amount thereof increases, a corresponding one of the valve springs 11 is compressed and the reactive force exerted by each of the valve springs 11 against the operation of a corresponding one of the exhaust valve opening/closing devices 90 increases. .

On the other hand, as is the case with the exhaust side, each of the intake valve opening/closing devices 100 is provided with corresponding ones of valve springs 21, corresponding ones of retainers 26 provided for the intake valves 20, corresponding ones of rocker arms 23, and corresponding ones of lash adjusters 22. An intake cam shaft 24 on which a plurality of cams 25 are formed is rotatably supported by the cylinder head 2. This intake cam shaft 24 is also rotated in a manner interlocking with the rotation of the output shaft of the engine. Unlike each of the exhaust valve opening/closing devices 90, each of the intake valve opening/closing devices 100 is provided with a corresponding one of intermediary drive mechanisms 50 that is located between a corresponding one of the cams 25 and corresponding ones of the rocker arms 23. Each of these intermediary drive mechanisms 50 has a corresponding one of input portions 51 and a corresponding one of pairs of output portions 52 as shown in FIG. 3. The input portions 51 and the output portions 52 are rockably supported by a support pipe 53 fixed to the cylinder head 2. Each of the rocker arms 23 is urged toward a corresponding one of the output portions 52 side due to urging forces of a corresponding one of the lash adjusters 22 and a corresponding one of the valve springs 21. Each of rollers 23a provided on intermediate regions of the rocker arms 23 abuts on an outer peripheral face of a corresponding one of the output portions 52. Thus, each of the input portion 51 is urged in a rocking manner counterclockwise Wl together with a corresponding one of the pairs of the output portions 52. Each of rollers 51a provided at tips of radially extended regions of the input portions 51 is pressed against an outer peripheral face of a corresponding one of the cams 25.

In each of the intake valve opening/closing devices 100 constructed as described above, when the cams 25 rotate during operation of the engine, each of the cams 25 presses a corresponding one of the input portions 51 while remaining in slidable contact with a corresponding one of the rollers 51a. A corresponding one of the pairs of the output portions 52 thereby rock around the support pipe 53. When each of the pairs of the output portions 52 rock, a corresponding one of the rocker arms 23 rocks around its region supported by a corresponding one of the lash adjusters 22. As a result, each of the intake valves 20 is driven by a corresponding one of the rocker arms 23 to be opened/closed. As the opening degree of each of the intake valves 20, namely, the lift amount thereof increases, a corresponding one of the valve springs 21 is compressed, and the reactive force exerted by each of the valve springs 21 against the operation of a corresponding one of the intake valve opening/closing devices 100 increases.

A control shaft 54 that can be driven along an axial direction thereof is inserted in the support pipe 53. This control shaft 54 is drivingly coupled to the input portions 51 and the output portions 52 via coupling members respectively. When the control shaft 54 is driven along the axial direction thereof, the input portions 51 and the output portions 52 rock relatively. Next, each of the intermediary drive mechanisms 50 for coupling the control shaft 54 to a corresponding one of the input portions 51 and a corresponding one of the pairs of the output portions 52 will be described in detail with reference to FIG. 3. FIG. 3 is a partially cutaway perspective view showing an internal structure of one of the intermediary drive mechanisms 50. As shown in FIG 3, the input portion 51 is provided between the pair of the output portions 52. A generally cylindrical communication space is formed inside the input portion 51 and the output portions 52. A helical spline 51h is formed on an inner peripheral face of the input portion 51. Helical splines 52h whose teeth are inclined reversely to those of the helical spline 5 Ih of the input portion 51 are formed on inner peripheral faces of the output portions 52 respectively.

A generally cylindrical slider gear 55 is provided in a space formed inside the input portion 51 and the output portions 52. A helical spline 55a meshing with the helical spline 5 Ih of the input portion 51 is formed on an axially central region of an outer periphery of the slider gear 55. A pair of helical splines 55b meshing with the helical splines 52h of the output portions 52 respectively are formed at both ends of the outer periphery of the slider gear 55.

Formed in an inner wall of this generally cylindrical slider gear 55 is a groove 55c extending along a circumferential direction thereof. A bush 56 is fitted in this groove 55c. This bush 56 can slide on an inner peripheral face of the groove 55c along a direction in which the groove 55c extends, but the groove 55c stops the bush 56 from being axially displaced relative to the slider gear 55.

The support pipe 53 is inserted in a through-space formed inside the slider gear 55, and the control shaft 54 is inserted in the support pipe 53. Formed in a tube wall of the support pipe 53 is a long hole 53a extending in an axial direction thereof. An engagement pin 57 for coupling the slider gear 55 and the control shaft 54 to each other through the long hole 53a is provided between the slider gear 55 and the control shaft 54. This engagement pin 57 is inserted at one end thereof in a recess portion (not shown) formed in the control shaft 54, and at the other end thereof in a through-hole 56a formed in the bush 56.

In each of the intermediary drive mechanisms 50 constructed as described above, when the control shaft 54 is displaced along the axial direction thereof, the slider gear 55 is displaced in the axial direction in a manner interlocking with the displacement of the control shaft 54. The helical spline 55a and the helical splines 55b that are formed on the outer peripheral face of the slider gear 55 mesh respectively with the helical spline 5 Ih and the helical splines 52h that are formed on the inner peripheral faces of the input portion 51 and the output portions 52. Therefore, when the slider gear 55 is displaced in the axial direction thereof, the input portion 51 and each of the output portions 52 rotate reversely to each other. As a result, the relative phase difference between the input portion 51 and each of the output portions 52 is changed, and the maximum lift amount of a corresponding one of the intake valves 20 is changed.

As shown in FIG. 2, a brushless motor 60 is provided at a base end (at the right end in FIG. 2) of the control shaft 54. This brushless motor 60 is connected to a microcomputer 70. The microcomputer 70 drivingly controls the brushless motor 60 to perform feedback control such that the maximum lift amount of the intake valves 20 coincides with a target lift amount corresponding to an operational state of the engine. The feedback control of the maximum lift amount by this microcomputer 70 will be described hereinafter with reference to FIGS. 4 to 6A and 6B. FIG. 4 is a block diagram showing the control shaft 54, the brushless motor 60, and the microcomputer 70. FIGS. 5A to 5H are timing charts showing modes of changes in output waveforms of respective sensors and respective count values.

As shown in FIG. 4, the control shaft 54 is coupled at the base end thereof to an output shaft 60a of the brushless motor 60 via a conversion mechanism 61. This conversion mechanism 61 serves to convert rotary motion of the output shaft 60a into rectilinear motion of the control shaft 54 in the axial direction thereof. That is, when the output shaft 60a is rotated positively/reversely, the rotation is converted into reciprocating motion of the control shaft 54 by the conversion mechanism 61. An engagement portion 54a is formed on the control shaft 54, and two stoppers 3a and 3b on which this engagement portion 54a can abut are formed on a cylinder head cover 3 of the internal combustion engine. The control shaft 54 can be driven between two drive limit positions (within a movable range) where the engagement portion 54a abut on the stoppers 3 a and 3 b respectively.

When the control shaft 54 is driven to the drive limit position where the engagement portion 54a abuts on the stopper 3a, namely, a mechanical upper-limit position of an operational range thereof (hereinafter referred to as a "Hi end"), the maximum lift amount becomes equal to its designed maximum value Bhi. On the other hand, when the control shaft 54 is driven to the drive limit position where the engagement portion 54a abuts on the stopper 3b, namely, a mechanical lower-limit position of the operational range thereof (hereinafter referred to as a "Lo end"), the maximum lift amount becomes equal to its designed minimum value Bio.

The brushless motor 60 is provided with three electric angle sensors Dl to D3, and a multipolar magnet (not shown) with eight poles that rotates integrally with the output shaft 60a in a manner corresponding to the electric angle sensors Dl to D3. These electric angle sensors Dl to D3 alternately output pulse-like signals shown in FIGS. 5A to 5C, namely, a logic high-level signal "H" and a logic low-level signal "L" in accordance with the magnetism of the multipolar magnet with the eight poles. In order to obtain the waveforms of these pulse signals, the three electric angle sensors Dl to D3 are arranged at angular intervals of 120° in the circumferential direction of the output shaft 60a. Accordingly, the edge of the pulse signal output from one of these electric angle sensors Dl to D3 is generated every time the output shaft 60a rotates by 45°. The pulse signal from one of these electric angle sensors Dl to D3 is respectively offset in phase toward an advancement side and a retardation side by a rotational angle of 30° of the output shaft 60a with respect to the pulse signals from the other electric angle sensors.

The brushless motor 60 is provided with two position sensors Sl and S2 functioning as rotary encoders, and a multipolar magnet (not shown) with 48 poles that rotates integrally with the output shaft 60a in a manner corresponding to the position sensors Sl and S2. These position sensors Sl and S2 alternately output pulse-like signals shown in FIGS. 5D and 5E, namely, the logic high-level signal "H" and the logic low-level signal "L" in accordance with the magnetism of the multipolar magnet with the 48 poles. As shown in FIGS. 5D and 5E, the pulse signal from the position sensor S2 is offset in phase by a rotational angle of 3.75° of the output shaft 60a with respect to the pulse signal from the position sensor Sl. In order to obtain the waveforms of these pulse signals, the position sensor Sl is arranged apart from the position sensor S2 by 176.25° in the circumferential direction of the output shaft 60a. Accordingly, the edge of the pulse signal output from one of the position sensors Sl and S2 is generated every time the output shaft 60a rotates by 7.5°. •

While the edge clearance of a resultant pulse signal of the electric angle sensors Dl to D3 is 15°, the edge clearance of a resultant pulse signal of the position sensors Sl and S2 is

3.75°. Accordingly, the edge of the resultant pulse signal of the position sensors Sl and

S2 is generated four times between a timing of generation of an edge of the resultant pulse signal of the electric angle sensors Dl to D3 and a subsequent timing of generation thereof.

The pulse signals output by these electric angle sensors Dl to D3 and these position sensors Sl and S2 are acquired by the microcomputer 70. This microcomputer 70 is equipped with a central processing unit (CPU) 71 for performing numerical calculation, information processing, and the like according to programs, a non-volatile memory (ROM) 72a for storing programs and data necessary for various types of control, a volatile memory (DRAM) 72b for temporarily storing input data and calculation results, and a rewritable non-volatile memory (EEPROM) 72c for storing a reference position obtained through learning control and the like. As is well known, when storing data into addresses of the DRAM 72b, the microcomputer 70 charges/discharges memory cells corresponding to the addresses respectively. Thus, the value of bit data on a bit corresponding to each of the memory cells is "1 " or "0". That is, while the value of bit data on the bit corresponding to a charged one of the memory cells is "1", the value of bit data on the bit corresponding to an uncharged one of the memory cells is "0".

Sensors for detecting the operational state of the engine, such as an accelerator sensor 73 for detecting the opening degree of an accelerator pedal of the vehicle, a crank angle sensor 74 for detecting the rotational phase of a crankshaft of the internal combustion engine, and the like are connected to the microcomputer 70. The microcomputer 70 sets a control target value of the maximum lift amount of the intake valves 20 on the basis of an operational state of the engine, and detects an actual value of the maximum lift amount of the intake valves 20 on the basis of pulse signals output by the aforementioned electric angle sensors Dl to D3 and the aforementioned position sensors Sl and S2. A procedure of detecting the actual value of the maximum lift amount of the intake valves 20 will be described hereinafter in detail with reference to FIGS. 5Ato 5H and FIGS. 6Aand 6B.

FIGS. 5 A to 5E respectively show the waveforms of pulse signals that are output from the electric angle sensors Dl to D3 and the position sensors Sl and S2 during rotation of the output shaft 60a of the brushless motor 60 as described above. FIGS. 5F to 5H respectively show patterns of changes in an electric angle count value E, a position count value P₅ and a stroke count value S in accordance with changes in the rotational angle of the brushless motor 60 during rotation thereof. FIG. 6A shows a relationship in correspondence between the patterns of the output signals of the electric angle sensors Dl to D3 and the electric angle count value E. FIG. 6B shows how the position count value P increases/decreases when edges of output signals of the position sensors Sl and S2 are generated.

First of all, the respective count values will be described.

The electric angle count value E is set on the basis of pulse signals of the electric angle sensors Dl to D3, and represents the rotational phase of the brushless motor 60. More specifically, as shown in FIG. 6A, depending on whether the logic high-level signal "H" or the logic low-level signal "L" is output from each of the electric angle sensors Dl to D3, the electric angle count value E is set to one of consecutive integral values within a range of "0" to "5", and stored into the DRAM 72b. The microcomputer -70 detects a rotational phase of the brushless motor 60 on the basis of the electric angle count value E stored in the DRAM 72b, and makes a switchover in the energization phase of the brushless motor 60 to rotate the brushless motor 60 positively/reversely. During positive rotation of the brushless motor 60, the electric angle count value E changes in a forward direction in the order of "0" -» "1 " → "2" -> "3" → "4" → "5" → "0". On the other hand, during reverse rotation of the brushless motor 60, the electric angle count value E changes in a reverse direction in the order of "5" -> "4" → "3" -» "2" → "1" → ¹¹O" → "5".

The position count value P represents the amount of displacement of the control shaft 54 from a reference position at the time of engine start after the internal combustion engine is started, that is, the history of changes in the maximum lift amount of the intake valves 20 from the reference value at the time of engine start. More specifically, the position count value P is incremented by "+1" or "-1" depending on whether a rising edge or a falling edge of a pulse signal is generated from one of the position sensors Sl and S2 and whether the logic high-level signal "H" or the logic low-level signal "L" is output from the other sensor (see FIG. 6B). In FIG. 6B₃ "t" represents a rising edge of a pulse signal, and "4" represents a falling edge of a pulse signal. The position count value P obtained by the execution of the process as described above is equal to a counted number of edges of pulse signals from the respective position sensors Sl and S2.

When the brushless motor 60 rotates positively, the position count value P is incremented by "1" every time an edge of a pulse signal is generated from each of the position sensors Sl and S2 shown in FIGS. 5D and 5E₃ and changes in a direction indicated by an arrow A according to a pattern shown in FIG. 5G. On the other hand, when the brushless motor 60 rotates reversely, the position count value P is decremented by "1" every time the edge of the aforementioned pulse signal is generated, and changes in a direction indicated by an arrow B according to the pattern shown in FIG. 56 This position count value P is reset to "0" when the operation of the internal combustion engine is stopped. Accordingly, the position count value P represents how much the position of the control shaft 54 has changed with respect to the reference position at the time of engine start, that is, how much the maximum lift amount of the intake valves 20 during the operation of the engine has changed with respect to an initial value at the time of engine start. The position count value P needs to be quickly incremented/decremented on the basis of the driving of the intake valve opening/closing devices 100, and hence is stored in the DRAM 72b. The stroke count value S represents the amount of displacement of the control shaft 54 from a reference position where the control shaft 54 has been displaced to the Lo end, that is, the actual value of the maximum lift amount. That is, as regards the initial setting of the stroke count value S, when the control shaft 54 is displaced to the Lo end, the microcomputer 70 sets the stroke count value S to "0". The microcomputer 70 adds the position count value P to the stroke count value S. Thus, the stroke count value S is updated to a value obtained through this addition. A final value of the stroke count value S at the time when the driving of the intake valve opening/closing devices 100 is stopped after the completion of engine stop is learned as a reference value Sg at the time when the operation of the engine is started next time, and stored into the EEPROM 72c. Accordingly, the microcomputer 70 calculates the stroke count value S, that is, the actual value of the maximum lift amount on the basis of the reference value Sg stored in the EEPROM 72c and the position count value P stored in the DRAM 72b. The microcomputer 70 then drivingly controls the brushless motor 60, thereby performing feedback control such that the difference between the actual value and the control target value set on the basis of the operational state of the engine becomes small. Thus, it is possible to change the maximum lift amount of the intake valves 20 to a value suited for the operational state of the engine and make improvements in the fuel consumption and output of the internal combustion engine.

When a difference is created between the detected value of the position count value P and the actual value thereof due to changes in sensor characteristics of the position sensors Sl and S2 or the like, a difference is created between the calculated value of the stroke count value S (i.e., the absolute position of the control shaft 54) and the actual value thereof. As a result, it may become impossible to perform the aforementioned feedback control of the maximum lift amount accurately.

In this case, however, the adverse effect of this difference can be suppressed by carrying out Lo end learning, which will be described below. That is, when a predetermined learning condition is fulfilled, for example, when changes in the sensor characteristics of the position sensors Sl and S2 are detected, the control shaft 54 is displaced to the Lo end. When it is determined that the control shaft 54 has reached the Lo end, the absolute position of the control shaft 54 is learned, and the position of the control shaft 54 calculated at that time is updated to the learned absolute position. Thus, even in the case where the sensor characteristics of the position sensors Sl and S2 change, the position of the control shaft 54 calculated on the basis of the outputs of the position sensors Sl and S2 can be made to coincide with the actual position of the control shaft 54.

However, the absolute position of the control shaft 54 corresponds to a valve characteristic such as the maximum lift amount of the intake valves 20 or the like. Therefore, when the control shaft 54 is displaced to the Lo end, the maximum lift amount of the intake valves 20 may change, and the amount of fuel injection calculated on the basis of the maximum lift amount may change needlessly.

In updating the calculated value of the absolute position of the control shaft 54 to the learned absolute position, when the calculated value changes, it is determined that the maximum lift amount of the intake valves 20 has changed. In the case where this erroneous determination is made, the amount of fuel injection controlled on the basis of the maximum lift amount is set to a value failing to correspond to the actual amount of intake air, and there is an apprehension that the air-fuel ratio of the engine may deviate from its target value.

Thus, in the control apparatus for the valve operating system according to this embodiment of the invention, the above-mentioned inconvenience is mitigated by adopting 008/001212

a processing that will be described below. A processing procedure followed in carrying out the Lo end learning will be -described hereinafter in detail with reference to a flowchart of FIG. 7.

A series of processings shown in FIG. 7 are repeatedly performed by the microcomputer 70 on a predetermined control cycle. In these processings, it is first determined whether or not a learning condition flag Fg is "on" (step SlO). This learning condition flag Fg is set "on" through another processing when a predetermined Lo end learning condition is fulfilled, for example, when the sensor characteristics of the position sensors S3 and S2 change. "When this learning condition flag Fg is "off' (step SlO: NO)₃ it is determined that the predetermined Lo end learning condition is not fulfilled, and the series of these processings are temporarily terminated. On the other hand, when the learning condition flag Fg is "on" (step SlO: YES), it is determined that the predetermined Lo end learning condition is fulfilled, and it is determined whether or not the cutting of fuel supply in the internal combustion engine is being carried out (step S20).

When it is determined that the cutting of fuel supply is not being carried out (step S20: NO), the series of these processings are temporarily terminated. On the other hand, when it is determined that the cutting of fuel supply is being carried out (step S20: YES)₅ the Lo end learning is carried out. In this processing of the Lo end learning, the stroke count value S is first calculated on the basis of the position count value P stored in the DRAM 72b and the reference value Sg stored in the EEPROM 72c, through an expression (1) shown below (step S30). Furthermore, a control target value St of the stroke count value is calculated through an expression (2) shown below, and feedback control of the maximum lift amount is performed (step S40).

S <- Sg+P ... (l)

St <- S-B ... (2)

In the expression (2), a decremental value B is a preset positive value. Thus, the control target value St is set smaller than the stroke count value S, and the control shaft 54 is driven to be displaced to the Lo end side. The magnitude of this decreraental value B is appropriately set such that the maximum driving force of the brushless motor 60 becomes smaller than during normal control, with a view to restricting the brushless motor 60 or a peripheral mechanism thereof from being overloaded. As a result, the maximum lift amount decreases, and the position count value P decreases.

It is then determined whether or not a change amount ΔP of the position count value P is smaller than a threshold ΔPO (step S50). When the change amount ΔP is larger than the threshold ΔPO, it is determined that the control shaft 54 is driven, and a return to the foregoing step S30 is made to continue to carry out the Lo end learning of the maximum lift amount. On the other hand, when the change amount ΔP is smaller than the threshold

ΔPO, it is determined that the control shaft 54 has reached the Lo end, and the stroke count value S at that time is immediately updated to a stroke count value corresponding to the Lo end ("0" in this embodiment of the invention) that is stored in the ROM 72a (step S60).

The position count value P is updated on the basis of the updated stroke count value S and the reference value Sg, through an expression (3) shown below (step S70).

P «~ S-Sg ... (3)

The learning condition flag Fg is then set "off' (step S80) to temporarily terminate the series of these processings.

One concrete example of the aforementioned processings will be described hereinafter with reference to FIG. 8. FIG. 8 is composed of timing charts respectively showing changes with time in the state of fuel cut control, the stroke count value S, and the position count value P.

As shown in FIG. 8, when the predetermined Lo end learning condition is fulfilled due to changes in the sensor characteristics of the position sensors Sl and S2 at a time Tl₅ the learning condition flag Fg is set "on" (step SlO: YES). Then, when it is determined that the control of fuel cut is being performed (step S20: YES), the Lo end learning is carried out.

That is, the stroke count value S is first calculated on the basis of the position count value P stored in the DRAM 72b and the reference value Sg (step S30). In this example, a difference δ is arisen between the calculated value of this stroke count value S and the actual value thereof due to changes in the sensor characteristics of the position sensors Sl and S2. The control target value St of the stroke count value S is then set smaller than the calculated value of the stroke count value S to perform feedback control of the maximum lift amount (step S40). As a result, the control shaft 54 is displaced to the Lo end, and the position count value P, the calculated value of the stroke count value S, and the actual value of the stroke count value S decrease.

When the control shaft 54 reaches the Lo end at a time T2 (step S50: YES), the stroke count value S is immediately updated to the stroke count value corresponding to the Lo end that is stored in the ROM 72a, namely, "O" (step S60). The position count value P stored in the DRAM 72b is then updated to a difference between the updated stroke count value S and the reference value Sg ("-Sg") (step S70), and the learning condition flag Fg is set "off¹ (step S80).

According to the foregoing embodiment of the invention described above, the following effects are obtained.

(1) When the predetermined learning condition is fulfilled during the cutting of fuel supply in the engine, the control shaft 54 is displaced to the Lo end and the absolute position of the control shaft 54 is learned. Therefore, the amount of fuel injection can be prevented from changing in displacing the control shaft 54 to the Lo end. The calculated value of the stroke count value S is then updated during the cutting of fuel supply in the engine when the Lo end position is learned during the cutting of fuel supply. Therefore, even when the stroke count value S changes in accordance with the updating thereof, the amount of fuel injection can be prevented from changing. As a result, the relationship between the valve characteristics and the amount of fuel injection can be restricted from changing. Therefore, the stroke count value S can be swiftly updated while suppressing the influence of sudden changes in the valve characteristics.

(2) The calculated value of the stroke count value S is immediately updated during the cutting of fuel supply when the Lo end learning is carried out during the cutting of fuel supply. Thus, the stroke count value S can be updated rather swiftly. Therefore, in comparison with the case where, for example, the calculated value of the stroke count value S is gradually updated, the relationship between the valve characteristics and the amount of fuel injection can be restrained from remaining inadequate as a result of the suspension of fuel cut control prior to the completion of the updating. In the foregoing embodiment of the invention, when the control shaft 54 reaches the Lo end, the stroke count value S is immediately updated to the stroke count value corresponding to the Lo end. However, the invention is not limited to this way of updating the stroke count value S. The stroke count value S may be gradually updated to the stroke count value corresponding to the Lo end as long as the updating of the stroke count value S can be completed during the execution of fuel cut control.

In the foregoing embodiment of the invention, the case where the invention is applied to the control apparatus for the valve operating system that displaces the control shaft 54 to the Lo end to update the calculated value of the stroke count value S to the stroke count value corresponding to the Lo end is exemplified. However, the invention is not limited to this case. The invention can also be applied basically in the same manner to a control apparatus for a valve operating system that displaces the control shaft 54 to the Hi end to update the calculated value of the stroke count value S to a stroke count value corresponding to the Hi end.

Claims

CLAIMS:

1. A control apparatus for a valve operating system having a control shaft driven within a movable range between a first end and a second end, and an actuator that drives the control shaft to change a valve characteristic of an internal combustion engine, comprising: a control portion that calculates an absolute position of the control shaft on a basis of a reference position and an amount of displacement of the control shaft from the reference position; a learning portion that displaces the control shaft to one of the first end and the second end to learn the absolute position of the control shaft when a predetermined learning condition is fulfilled during execution of fuel cut control in the internal combustion engine; and a learned value updating portion that updates the absolute position of the control shaft during execution of the fuel cut control in the internal combustion engine when the absolute position is learned by the learning portion.

2. The control apparatus according to claim 1, wherein the learned value updating portion immediately updates the absolute position when the absolute position is learned by the learning portion during the execution for the fuel cut control in the internal combustion engine.

3. The control apparatus according to claim 1, wherein the learned value updating portion updates the absolute position at a point of time when the absolute position is learned by the learning portion during the execution for the fuel cut control in the internal combustion engine.

4. The control apparatus according to claim 1 , wherein the learned value updating portion updates the absolute position within a period which is shorter than a predetermined period after the absolute position is learned by the learning portion during the execution for the fuel cut control in the internal combustion engine.

5. The control apparatus according to any one of claims 1 to 4, further comprising: a position sensor that detects a position of the control shaft, wherein the learning portion determines that the predetermined learning condition is fulfilled, when a sensor characteristic of the position sensor is changed.

6. The control apparatus according to any one of claims 1 to 5, wherein: the actuator drives the control shaft in an axial direction thereof; and the control shaft changes phases of an input portion abutting on an outer peripheral face of a cam shaft of the internal combustion engine and an output portion abutting on a rocker arm of the internal combustion engine by the actuator.

7 The control apparatus according to any one of claims 1 to 6, wherein the learning portion determines that the control shaft has reached to one of the first end and the second end, when an amount of displacement of the control shaft in the axial direction thereof is smaller than a predetermined amount.

8. A control method for a valve operating system having a control shaft driven within a movable range between a first end and a second end, and an actuator that drives the control shaft to change a valve characteristic of an internal combustion engine, comprising: calculating an absolute position of the control shaft on a basis of a reference position of the control shaft and an amount of displacement of the control shaft from the reference position; displacing the control shaft to one of the first end and the second end to learn the absolute position of the control shaft, when a predetermined learning condition is fulfilled during execution of fuel cut control in the internal combustion engine; and updating the absolute position during execution of the fuel cut control in the internal combustion engine when the absolute position of the control shaft is learned.