US20100059006A1

US20100059006A1 - Variable Valve Operating Apparatus

Info

Publication number: US20100059006A1
Application number: US11/988,502
Authority: US
Inventors: Toshiyuki Maehara
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2005-09-28
Filing date: 2006-09-22
Publication date: 2010-03-11
Also published as: CN101273192A; DE112006002253T5; WO2007037177A1; JPWO2007037177A1

Abstract

The present invention relates to a variable valve operating apparatus having a switching mechanism for switching between a dual valve variable control mode and a single valve variable control mode, and enhances the durability of the switching mechanism.

In an idle state prevailing before a vehicle starts moving, the operating state of an internal combustion engine is in a single valve small lift region (point A). In this instance, the single valve variable control mode prevails. After the vehicle starts moving, the operating state changes from point A through point B to point C and switches to a dual valve great lift region. Subsequently, when an accelerator pedal is released with a clutch disengaged for upshifting, the operating state reverts to point A in the single valve small lift region. In the above situation, as the operating state remains in the dual valve great lift region for a short period of time, a switch to the dual valve variable control mode does not constitute a considerable advantage. Therefore, the switch to the dual valve variable control mode is prohibited when the operating state changes from point B to point C.

Description

TECHNICAL FIELD

The present invention relates to a variable valve operating apparatus, and more particularly to a variable valve operating apparatus that is capable of mechanically changing a valve opening amount.

BACKGROUND ART

It is known that a conventional variable valve operating apparatus described, for instance, in Patent Document 1 mechanically changes the lift amount and operating angle of a valve in accordance with the operating state of an internal combustion engine.
In the variable valve operating apparatus described in Patent Document 1, two rotary cams are installed over a camshaft. Two intake valves are provided for a single cylinder. A first intake valve is opened and closed by a first rotary cam. A second intake valve is opened and closed by a second rotary cam. A variable valve transmission mechanism, which includes a four-joint link mechanism, is positioned between the first rotary cam and the first intake valve and between the second rotary cam and the second intake valve.
The four-joint link mechanism of the above variable valve operating apparatus includes an input arm, which has an input section that abuts against the rotary cams; a transmission arm, which is swingably coupled to the input arm; a swing arm, which is swingably coupled to the transmission arm, can swing on a rotation control shaft, and receives driving force from the rotary cams and transmits it to an output section that opens/closes the intake valves; and a control arm, which rotates on the rotation control shaft and is swingably coupled to the input arm. The operating angles and lift amounts of the intake valves can be mechanically changed by controlling the posture of the four-joint link mechanism to change the positional relationship between the rotary cams and input section.
Further, the above variable valve operating apparatus includes a coupling mechanism for coupling a first link mechanism, which is a four-joint link mechanism related to the first intake valve, to a second link mechanism, which is a four-joint link mechanism related to the second intake valve, and a mechanism for keeping the posture of the second link mechanism at the time of uncoupling so as to maximize the operating angle of the second intake valve. The coupling mechanism includes a through-hole, which is made in the control arm of each four-joint link mechanism, and a coupling pin, which is to be inserted into the through-hole. The mechanism for keeping the posture of the second link mechanism at the time of uncoupling includes a through-hole made in a fixed plate, a through-hole made in a second control arm (the control arm for the second link mechanism), and the aforementioned coupling pin.
The coupling pin is constantly inserted in the through-hole in the second control arm, and can move toward a first control arm, which is the control arm for the first link mechanism, or toward the fixed plate while being inserted in the through-hole in the second control arm. When the coupling pin moves toward the first control arm and goes into the through-hole in the first control arm, the second control arm is coupled to the first control arm via the coupling pin. When the control arms are coupled together, the first and second link mechanisms maintain the same posture. In this instance, control is exercised so that the valve opening amounts of the first and second valves are equal.
When, on the contrary, the coupling pin moves toward the fixed plate and goes into the through-hole in the fixed plate, the second control arm is coupled to the fixed plate via the coupling pin. When the second control arm is coupled to the fixed plate, the second link mechanism maintains a predetermined posture. In this instance, when the posture of the first link mechanism is controlled to change the positional relationship between the rotary cams and input section, only the valve opening amount of the first valve can be mechanically changed while the valve opening amount of the second valve is fixed.
In other words, the above variable valve operating apparatus can select a mode in which the first and second intake valves have the same valve opening amount or a mode in which the first and second intake valves differ in the valve opening amount. The valve opening amounts, particularly the lift amounts, of the first and second intake valves can then be made different from each other. Since this gives rise to different intake flow rates, a swirl flow can be created within a combustion chamber to assure increased combustion stability in the combustion chamber.
Patent Document 1: Japanese Patent Laid-open No. 2004-100555

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

As implied above, the above variable valve operating apparatus can choose between a dual valve variable control mode in which the valve opening amounts of the first and second intake valves are varied and a single valve variable control mode in which only the valve opening amount of the first intake valve is varied with the valve opening amount of the second intake valve fixed. When switching from the dual valve variable control mode to the single valve variable control moved, it is necessary to perform two operations, that is, extract the coupling pin from the pin hole in the first control arm and insert the coupling pin into the pin hole in the fixed plate. When, on the other hand, switching from the single valve variable control mode to the dual valve variable control mode, it is necessary to perform two operations, that is, extract the coupling pin from the pin hole in the fixed plate and insert the coupling pin into the pin hole in the first control arm.
The internal combustion engine described above switches between the dual and single valve variable control modes in accordance with the operating state. In a low engine speed/low load region, for instance, the single valve variable control mode is selected because it is demanded that a swirl be created within a cylinder to provide combustion improvement. In a high engine speed/high load region, on the other hand, the dual valve variable control mode is selected because it is demanded that a large amount of air be taken in. More specifically, a control device for the internal combustion engine stores rules for dividing an operating region into a dual valve variable control region, for which the dual valve variable control mode should be selected, and a single valve variable control region, for which the single valve variable control mode should be selected. When the operating state of the internal combustion engine shifts from one region to another, the control device switches between the dual and single valve variable control modes accordingly.
However, if the control device frequently switches between the dual and single valve variable control modes, it is likely that the durability of a switching mechanism will be adversely affected due to premature wear of the aforementioned coupling pin and pin hole, which constitute the switching mechanism. Further, such frequent switching might result in switching failure. If switching failure should occur, proper valve opening characteristics will not be obtained. This results in the failure to obtain expected fuel efficiency and driveability.
The present invention has been made in view of the above circumstances. An object of the present invention is to provide a variable valve operating apparatus that includes a switching mechanism for switching between the dual and single valve variable control modes and improves the durability of the switching mechanism.

ADVANTAGES OF THE INVENTION

Means for Solving the Problem

First aspect of the present invention is a variable valve operating apparatus comprising:
a valve mechanism having a switching mechanism for switching between a dual valve variable control mode in which the valve opening amounts of a first valve and a second valve, which are provided for the same cylinder and of the same type, are varied continuously or in multiple steps and a single valve variable control mode in which the valve opening amount of the first valve is varied continuously or in multiple steps with the valve opening amount of the second valve fixed;
storage means for storing rules for dividing an operating region of an internal combustion engine into a dual valve variable control region, for which the dual valve variable control mode should be selected, and a single valve variable control region, for which the single valve variable control mode should be selected;
normal control means for causing the switching mechanism to perform a switching operation in accordance with the rules;
condition judgment means for judging, when the operating state of the internal combustion engine switches from the dual valve variable control region to the single valve variable control region or vice versa, whether a predefined condition is established for anticipating that the operating state will revert to the previous region within a short period of time; and
disable means for disabling the switching operation when the predefined condition is established.
Second aspect of the present invention is the variable valve operating apparatus according to the first aspect, wherein the predefined condition denotes a condition where a predetermined period of time has not elapsed since a gear shift by a transmission positioned between the internal combustion engine and vehicle driving wheels.
Third aspect of the present invention is the variable valve operating apparatus according to the first aspect, wherein the predefined condition denotes a condition where a transmission positioned between the internal combustion engine and vehicle driving wheels is shifted to neutral or park.
Fourth aspect of the present invention is the variable valve operating apparatus according to any one of the first to the third aspects, further comprising:
enable means for enabling the switching operation if the operating state of the internal combustion engine does not revert to a previous region within a predetermined period of time after a switch from the dual valve variable control region to the single valve variable control region or vice versa.
Fifth aspect of the present invention is the variable valve operating apparatus according to any one of the first to the fourth aspects, further comprising:
measurement means for measuring the number of times the switching operation was disabled or the cumulative time during which the switching operation was disabled; and
permission means which, when a predetermined value is exceeded by the number of times the switching operation was disabled or the cumulative time during which the switching operation was disabled, permits the switching mechanism to perform a switching operation no matter whether the predefined condition is established.
Sixth aspect of the present invention is the variable valve operating apparatus according to any one of the first to the fifth aspect, further comprising:
valve opening amount limitation means for limiting a target valve opening amount when the switching operation is disabled by the disable means.
Seventh aspect of the present invention is the variable valve operating apparatus according to the sixth aspect,
wherein the valve mechanism includes a main cam, which drives both the first valve and the second valve in the dual valve variable control mode and drives only the first valve in the single valve variable control mode; and a sub-cam, which drives the second valve in the single valve variable control mode; and
wherein the valve opening amount limitation means limits the target valve opening amount so as to keep the sub-cam from leaving a mating member for the sub-cam when the disable means disables a switch from the single valve variable control mode to the dual valve variable control mode to maintain the single valve variable control mode.

EFFECTS OF THE INVENTION

According to the first aspect of the present invention, the switching mechanism can switch between the dual valve variable control mode and single valve variable control mode. This switching operation is performed in accordance with rules for dividing the operating region of the internal combustion engine into the dual valve variable control region and single valve variable control region depending on the operating state of the internal combustion engine. However, the switching operation is disabled if, when the operating state switches from the dual valve variable control region to the single valve variable control region or vice versa, a predefined condition is established for anticipating that the operating state will revert to the previous region within a short period of time. Therefore, the first aspect of the present invention makes it possible to reduce the frequency of switching operation by avoiding unnecessary switching operations. Consequently, the durability of the switching mechanism can be increased by avoiding undue wear and scratching of the switching mechanism. Further, the possibility of switching failure can be reduced to constantly implement valve opening characteristics according to the operating state and properly obtain satisfactory fuel efficiency characteristics, exhaust characteristics, and driveability.
According to the second aspect of the present invention, it is possible to absolutely avoid an unnecessary switching operation that is likely to take place immediately after gear shifting by the transmission. Therefore, the frequency of switching operation can be reduced while the vehicle is moving.
According to the third aspect of the present invention, it is possible to absolutely avoid an unnecessary switching operation during a free acceleration (so-called racing) operation, which is performed while the transmission is in neutral or parking position. Therefore, the frequency of switching operation can be reduced during free acceleration.
If the operating state of the internal combustion engine does not revert to a previous region within a short period of time after it is changed from the dual valve variable control region to the single valve variable control region or vice versa, the fourth aspect of the present invention can enable the switching operation and perform the switching operation. Therefore, if the switching operation is actually needed in a situation where it is assumed that no switching operation is needed, the switching operation can be performed to implement preferred valve opening characteristics.
When a predetermined value is exceeded by the number of times the switching operation was disabled or the cumulative time during which the switching operation was disabled, the fifth aspect of the present invention can perform the switching operation even in a situation where a condition for anticipating that the switching operation is unnecessary is established. Therefore, the switching operation can be performed in any situation with frequency required for maintaining the function of the switching mechanism. This makes it possible to avoid problems, for instance, by preventing the switching mechanism from binding due to long-term inactivity.
When the operation for switching between the dual valve variable control mode and single valve variable control mode is disabled, the sixth aspect of the present invention can limit the target valve opening amount. This makes it possible to absolutely avoid noise and other problems that may arise when the switching operation is disabled.
When the operation for switching from the single valve variable control mode to the dual valve variable control mode is disabled to maintain the single valve variable control mode in a situation where the valve mechanism includes the main cam, which drives both the first valve and the second valve in the dual valve variable control mode and drives only the first valve in the single valve variable control mode, and the sub-cam, which drives the second valve in the single valve variable control mode, the seventh aspect of the present invention can limit the target valve opening amount so that the sub-cam does not leave its mating member. Since this feature absolutely prevents the sub-cam from leaving the mating member and coming back into contact (colliding) with it, it is possible to absolutely avoid noise generation from collision and prevent the surfaces of the sub-cam and its mating member from being damaged.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the configuration of a system that includes a variable valve operating apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view illustrating the configuration of a valve mechanism included in the variable valve operating apparatus according to the first embodiment of the present invention.

FIG. 3 illustrates the configuration of a variable valve mechanism included in the valve mechanism shown in FIG. 2.

FIG. 4 is an exploded perspective view illustrating variable valve mechanisms and fixed valve mechanism shown in FIG. 2.

FIG. 5 is a schematic diagram illustrating the configuration of a hydraulic system for operating a switching pin.

FIG. 6 shows a map for switching between a dual valve variable control mode and a single valve variable control mode.

FIG. 7 shows a map for switching between the dual valve variable control mode and the single valve variable control mode.

FIG. 8 is a flowchart illustrating a routine that is executed by the first embodiment of the present invention.

FIG. 9 is a flowchart illustrating a routine that is executed by a second embodiment of the present invention.

FIG. 10 is a flowchart illustrating a routine that is executed by a third embodiment of the present invention.

FIG. 11 shows valve lift curves of a first intake valve and a second intake valve.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

System Configuration

FIG. 1 illustrates the configuration of a system that includes a variable valve operating apparatus according to a first embodiment of the present invention. The system shown according to the first embodiment includes an internal combustion engine 1, which is mounted in a vehicle as a driving source. The internal combustion engine 1 includes a plurality of cylinders 2. FIG. 1 shows only one of the plurality of cylinders 2.
The internal combustion engine 1 also includes a cylinder block 4. The cylinder block 4 houses a piston 3 within a cylinder. The piston 3 is connected to a crankshaft 5 via a connecting rod. A crank angle sensor 6 is installed near the crankshaft 5. The crank angle sensor 6 is configured to detect the rotation angle of the crankshaft 5.
A cylinder head 8 is attached to the top of the cylinder block 4. A combustion chamber 10 is formed by the space between the upper surface of the piston 3 and the cylinder head 8. The cylinder head 8 is provided with an ignition plug 11, which ignites an air-fuel mixture in the combustion chamber 10.
The cylinder head 8 has an intake port 12 that communicates with the combustion chamber 10. The joint between the intake port 12 and combustion chamber 10 is provided with an intake valve 14. A valve mechanism 18 is installed between the intake valve 14 and an intake cam 16 on an intake camshaft 15. The valve mechanism 18 will be described in detail later.
The intake port 12 is connected to an intake path 19. An injector 20 is installed near the intake port 12 to inject fuel into the intake port 12. A surge tank 21 is positioned in the middle of the intake path 19.
A throttle valve 22 is installed upstream of the surge tank 21. The throttle valve 22 is an electronically-controlled valve that is driven by a throttle motor 23. The throttle valve 22 is driven in accordance with an accelerator opening AA, which is detected by an accelerator opening sensor 24. A throttle opening sensor 25 is installed near the throttle valve 22. The throttle opening sensor 25 is configured to detect a throttle opening TA. An air flow meter 26 is installed upstream of the throttle valve 22. The air flow meter 26 is configured to detect an intake air amount Ga. An air cleaner 27 is installed upstream of the air flow meter 26.
Further, the cylinder head 8 has an exhaust port 28 that communicates with the combustion chamber 10. The joint between the exhaust port 28 and combustion chamber 10 is provided with an exhaust valve 29. The exhaust port 28 is connected to an exhaust path 30. An air-fuel ratio sensor 31 is installed in the exhaust path 30 to detect an exhaust air-fuel ratio.
The system according to the present embodiment also includes an ECU (Electronic Control Unit) 60 as a control device. The output end of the ECU 60 is connected, for instance, to a discharge valve 84 (see FIG. 5), which will be described later, in addition to the ignition plug 11, valve mechanism 18, injector 20, and throttle motor 23. The input end of the ECU 60 is connected, for instance, to the crank angle sensor 6, throttle opening sensor 25, accelerator opening sensor 24, air flow meter 26, and air-fuel ratio sensor 31. In accordance with outputs generated by the sensors, the ECU 60 exercises control over the entire internal combustion engine such as fuel injection control and ignition timing control.
A transmission (not shown) is positioned between the internal combustion engine 1 and driving wheels of the vehicle. The ECU 60 is also connected to a shift position sensor 62, which detects the position to which the transmission is shifted. The transmission may be of either a manual type or an automatic type.

[Configuration of Variable Valve Train]

FIG. 2 is a perspective view illustrating the configuration of the valve mechanism 18 included in the variable valve operating apparatus according to the present embodiment.
As shown in FIG. 2, the intake camshaft 15 has two intake cams (a first intake cam 16 and a second intake cam 17) for each cylinder. Two intake valves (a first intake valve 14L and a second intake valve 14R) are positioned so that the first intake valve 14L and the second intake valve 14R are left-right symmetrical with respect to the first intake cam 16. Variable valve mechanisms 40L, 40R, which coordinate the lifting motions of the intake valves 14L, 14R with the rotary motion of the first intake cam 16, are respectively positioned between the first intake cam 16 and the intake valves 14L, 14R. Meanwhile, the second intake cam 17 is positioned so that the second intake valve 14R is sandwiched between the second intake cam 17 and the first intake cam 16. A fixed valve mechanism 70 is positioned between the second intake cam 17 and the second intake valve 14R to coordinate the lifting motion of the second intake valve 14R with the rotary motion of the second intake cam 17. The valve mechanism 18 is configured to select either the variable valve mechanism 40R or the fixed valve mechanism 70 as a coordination destination for the lifting motion of the second intake valve 14R.

(1) Detailed Configuration of Variable Valve Mechanism

FIG. 3 illustrates the configuration of a variable valve mechanism 40 in the valve mechanism 18 shown in FIG. 2. More specifically, FIG. 3 shows the variable valve mechanism 40 as viewed in the axial direction of the intake camshaft 15. Since the left- and right-hand variable valve mechanisms 40L, 40R are basically symmetrical with respect to the first intake cam 16, their configuration will be described without distinguishing between the left- and right-hand variable valve mechanisms 40L, 40R. In this document and accompanying drawings, the term “variable valve mechanism 40” is used when there is no need to distinguish between the left- and right-hand variable valve mechanisms 40L, 40R. Similarly, the symbols L and R, which respectively indicate left- and right-hand parts, are not attached to the names of the component parts of the variable valve mechanisms 40L, 40R, the intake valves 14L, 14R, and other symmetrically arranged parts except when it is necessary to distinguish between them.
As shown in FIG. 3, the valve mechanism 18 includes a rocker arm 35 that presses the intake valve 14 in the opening direction. The variable valve mechanism 40 is positioned between the first intake cam 16 and rocker arm 35. The variable valve mechanism 40 is configured to continuously vary the coordination between the rotary motion of the first intake cam 16 and the swing motion of the rocker arm 35.
The variable valve mechanism 40 includes a control shaft 41 that is positioned in parallel with the intake camshaft 15. A control arm 42 is fastened to the control shaft 41 with a bolt 43. A part of the control arm 42 projects in the radial direction of the control shaft 41. An intermediate arm 44 is mounted on the projection of the control arm 42 with a pin 45. The pin 45 is positioned eccentrically relative to the center of the control shaft 41. Therefore, the intermediate arm 44 swings on the pin 45.
A swing cam arm 50 is swingably supported by the control shaft 41. The swing cam arm 50 has a slide surface 50 a, which faces the first intake cam 16. The slide surface 50 a is formed so as to come into contact with a second roller 53. The slide surface 50 a is curved so that its distance to the first intake cam 16 gradually decreases when the second roller 53 moves from the leading end of the swing cam arm 50 toward the axial center of the control shaft 41. The swing cam arm 50 also has a swing cam surface 51, which is positioned opposite the slide surface 50 a. The swing cam surface 51 includes a nonoperating surface 51 a and an operating surface 51 b. The nonoperating surface 51 a is formed so that its distance from the swing center of the swing cam arm 50 is fixed. The operating surface 51 b is formed so that its distance from the axial center of the control shaft 41 increases with an increase in the distance to the nonoperating surface 51 a.
A first roller 52 and the second roller 53 are positioned between the slide surface 50 a and the circumferential surface of the first intake cam 16. More specifically, the first roller 52 is positioned so as to come into contact with the circumferential surface of the first intake cam 16, whereas the second roller 53 is positioned so as to come into contact with the slide surface 50 a of the swing cam arm 50. The first and second rollers 52, 53 are both rotatably supported by a coupling shaft 54 that is fastened to the leading end of the intermediate arm 44. Since the intermediate arm 44 swings on the pin 45, these rollers 52, 53 swing along the slide surface 50 a and the circumferential surface of the first intake cam 16 while maintaining a fixed distance from the pin 45.
Further, a spring seat 50 b is formed on the swing cam arm 50. One end of a lost motion spring 38 is engaged with the spring seat 50 b. The other end of the lost motion spring 38 is fastened to a stationary part of the internal combustion engine. The lost motion spring 38 is a compression spring. The force received from the lost motion spring 38 presses the slide surface 50 a of the swing cam arm 50 against the second roller 53 and the first roller 52 against the first intake cam 16. This positions the first and second rollers 52, 53 so that they are sandwiched between the slide surface 50 a and the circumferential surface of the first intake cam 16.
The aforementioned rocker arm 35 is positioned below the swing cam arm 50. A rocker roller 36 is attached to the rocker arm 35 so that the rocker roller 36 faces the swing cam surface 51. The rocker roller 36 is rotatably mounted on the middle part of the rocker arm 35. One end of the rocker arm 35 abuts against a valve shaft 14 a of the valve 14, and the other end of the rocker arm 35 is rotatably supported by a hydraulic lash adjuster 37. When a lifting operation is conducted, a valve spring (not shown) pushes the valve shaft 14 a in a closing direction, that is, in a direction of pushing up the rocker arm 35. The rocker roller 36 is pressed against the swing cam surface 51 of the swing cam arm 50 by the force of the valve spring and by the hydraulic lash adjuster 37.
According to the configuration of the variable valve mechanism 40 described above, the pushing force of the first intake cam 16 is transmitted to the slide surface 50 a via the first and second rollers 52, 53 as the first intake cam 16 rotates. When this moves the contact between the swing cam surface 51 and rocker roller 36 from the nonoperating surface 51 a to the operating surface 51 b, the rocker arm 35 is pushed downward to open the valve 14.
Further, when the rotational position of the control shaft 41 changes, the configuration of the variable valve mechanism 40 changes the position of the second roller 53 on the slide surface 50 a, thereby changing the swing range of the swing cam arm 50 for lifting motion. More specifically, when the control shaft 41 rotates counterclockwise in FIG. 3, the position of the second roller 53 on the slide surface 50 a moves toward the leading end of the swing cam arm 50. The rotation angle of the swing cam arm 50 that is required between the instant at which the swing cam arm 50 starts a swing motion upon receipt of pushing force from the first intake cam 16 and the instant at which the rocker arm 35 actually begins to be pushed then increases as the control shaft 41 rotates counterclockwise in FIG. 3. In other words, the operating angle and lift amount of the valve 14 can be decreased by rotating the control shaft 41 counterclockwise in FIG. 3. On the contrary, clockwise rotation of the control shaft 41 increases the operating angle and lift amount of the valve 14.
As described above, the variable valve mechanism 40 according to the present embodiment varies both the operating angle and lift amount of the valve 14. In this document, the operating angle and lift amount are collectively referred to as a “valve opening amount.” It should be noted, however, that the variable valve mechanism according to the present invention may alternatively be configured to vary either the operating angle or the lift amount.

(2) Detailed Configuration of Fixed Valve Mechanism

The configuration of the fixed valve mechanism 70 will now be described in detail with reference to FIGS. 2 and 4. FIG. 4 is an exploded perspective view illustrating the variable valve mechanism 40 and fixed valve mechanism 70 shown in FIG. 2.
As shown in FIG. 2, the fixed valve mechanism 70 is positioned between the second intake cam 17 and the second swing cam arm 50R. The fixed valve mechanism 70 coordinates the swing motion of the second swing cam arm 50R with the rotary motion of the second intake cam 17. The fixed valve mechanism 70 includes a great lift arm 71, which is driven by the second intake cam 17, and an arm coupling mechanism 72 (see FIG. 4), which couples the great lift arm 71 to the second swing cam arm 50R. The arm coupling mechanism 72 includes a switching pin 74, a hydraulic chamber 75, a pin hole 76, a return spring 77, and a piston 78, which will be described later.
The great lift arm 71, which is mounted on the control shaft 41 and positioned next to the second swing cam arm 50R, can swing independently of the second swing cam arm 50R. An input roller 73, which comes into contact with the circumferential surface of the second intake cam 17, is rotatably supported by the great lift arm 71.
As shown in FIG. 4, a spring seat 71 a is formed on the great lift arm 71. As is the case with the aforementioned swing cam arm 50, a lost motion spring (not shown) is engaged with the spring seat 71 a. The force of the lost motion spring presses the input roller 73 against the circumferential surface of the second intake cam 17.
The great lift arm 71 includes the switching pin 74, which can be inserted into and extracted from the second swing cam arm 50R. The great lift arm 71 is provided with the hydraulic chamber 75, which has an opening that is positioned toward the second swing cam arm 50R. The switching pin 74 is fitted into the hydraulic chamber 75. The hydraulic chamber 75 is connected to a hydraulic system that will be described later. When the hydraulic system raises the hydraulic pressure in the hydraulic chamber 75, the resulting hydraulic pressure pushes the switching pin 74 out of the hydraulic chamber 75 and toward the second swing cam arm 50R.
Meanwhile, the second swing cam arm 50R is provided with the pin hole 76, which has an opening that is positioned toward the great lift arm 71. The switching pin 74 and pin hole 76 are equidistant from the center of the control shaft 41. From bottom to top, items placed in the pin hole 76 are the return spring 77 and the piston 78 that serves as a lifter.
FIG. 5 is a schematic diagram illustrating the configuration of the hydraulic system for operating the switching pin 74. As shown in FIG. 5, an oil path 81 is formed in the control shaft 41. The oil path 81 is connected to the hydraulic chamber 75, a sliding gap between the control shaft 41 and the great lift arm 71, and a sliding gap between the control shaft 41 and the second swing cam arm 50R. The oil path 81 is also connected to a pump 82. A discharge path 83 is connected to the middle of the oil path 81. The discharge path 83 is provided with the discharge valve 84. Further, an orifice 85 is installed downstream of the discharge valve 84 in the discharge path 83.
Lubricating oil pressurized by the pump 82 is supplied to the above sliding gaps through the oil path 81. Part of the lubricating oil flowing in the oil path 81 is supplied to the hydraulic chamber 75. Therefore, the hydraulic pressure in the hydraulic chamber 75 can be raised. Meanwhile, opening the discharge valve 84 discharges the lubricating oil from the discharge path 83. This lowers the hydraulic pressure in the hydraulic chamber 75. The switching pin 74 can be operated by controlling the hydraulic pressure in the hydraulic chamber 75.

Features of First Embodiment

Single Valve Variable Control Mode

The great lift arm 71 constantly swings as it is driven by the second intake cam 17. However, while the base circle of the second intake cam 17 is in contact with the input roller 73, the great lift arm 71 is momentarily stationary. The second swing cam arm 50R also swings as it is driven by the first intake cam 16. However, while the base circle of the first intake cam 16 is in contact with the first roller 52, the second swing cam arm 50R is momentarily stationary. The periods during which the great lift arm 71 and the second swing cam arm 50R are stationary overlap with each other. In other words, there is a period during which the great lift arm 71 and the second swing cam arm 50R are simultaneously stationary.
The angle of the second swing cam arm 50R in the above stationary state varies with the rotational position of the control shaft 41. Therefore, there is a rotational position of the control shaft 41 at which the switching pin 74 aligns with the pin hole 76 while the great lift arm 71 and the second swing cam arm 50R are stationary. This rotational position of the control shaft 41 is hereinafter referred to as the “pin switching position.” In the valve mechanism 18, the pin hole 76 aligns with the switching pin 74 when the rotational position of the control shaft 41 agrees with the pin switching position. In this state, therefore, the arm coupling mechanism 72 can perform a switching operation as described below.
When the pin hole 76 aligns with the switching pin 74, the switching pin 74 abuts against the piston 78. If, in this state, the force exerted by the hydraulic pressure in the hydraulic chamber 75 to push the switching pin 74 is greater than the force exerted by the return spring 77 to push the piston 78, the switching pin 74 enters the pin hole 76 to push the piston 78 all the way into the pin hole 76. In other words, the switching pin 74 can be inserted into the pin hole 76 by allowing the hydraulic system to raise the hydraulic pressure in the hydraulic chamber 75. When the switching pin 74 is inserted into the pin hole 76, the second swing cam arm 50R is coupled to the great lift arm 71. The coordination destination for the lifting motion of the second intake valve 14R then changes from the variable valve mechanism 20R to the fixed valve mechanism 70.
In the above instance, the rotary motion of the intake camshaft 15 is transmitted from the second intake cam 17 to the second swing cam arm 50R via the great lift arm 71. The valve opening amount of the second intake valve 14R is mechanically determined by the shapes of the second intake cam 17, great lift arm 71, and second swing cam arm 50R and the positional relationship between them. It is constantly fixed as predetermined (to provide a great lift and large operating angle) irrespective of the rotational position of the control shaft 41. Meanwhile, the first intake cam 16 transmits the rotary motion of the first intake cam 16 to the first swing cam arm 50L via the first and second rollers 52, 53L. Consequently, the valve opening amount of the first intake valve 14L varies with the rotational position of the control shaft 41.
In this document, a state in which the valve opening amount of the first intake valve 14L varies with the rotational position of the control shaft 41 while the valve opening amount of the second intake valve 14R remains large as described above is referred to as the “single valve variable control mode.” In the single valve variable control mode, it is possible to provide the second intake valve 14R with a great lift and the first intake valve 14L with a small lift. This causes the second intake valve 14R to flow a large amount of air to the cylinder and the first intake valve 14L to flow a small amount of air to the cylinder. As the air flow rates differ as mentioned above, a swirl flow can be created within the cylinder. Creating the swirl flow provides combustion improvement in a low engine speed/low load region.

(Dual Valve Variable Control Mode)

The switching pin 74 can be extracted from the pin hole 76 by lowering the hydraulic pressure in the hydraulic chamber 75 when the pin hole 76 aligns with the switching pin 74. The great lift arm 71 is then uncoupled from the second swing cam arm 50R. Thus, the coordination destination for the lifting motion of the second intake valve 14R can be changed from the fixed valve mechanism 70 to the variable valve mechanism 20R.
In the above instance, the rotary motion of the camshaft 15 is transmitted from the first intake cam 16 to the slide surfaces 50 a of the first and second swing cam arms 50L, 50R via the first and second rollers 52, 53. Therefore, the valve opening amounts of the first and second intake valves 14L, 14R both vary in accordance with the rotation of the control shaft 41. Consequently, the valve opening amounts of the first and second intake valves 14L, 14R can be both varied in accordance with the rotational position of the control shaft 41. In this document, a state in which the valve opening amounts of the first and second intake valves 14L, 14R are both variable as described above is referred to as the “dual valve variable control mode.”
The ECU 60 switches between the dual valve variable control mode and single valve variable control mode in accordance with the operating state (more specifically, the engine speed NE and load) of the internal combustion engine 1. FIG. 6 shows a switching map that is stored in the ECU 60 and used for switching between the dual valve variable control mode and single valve variable control mode. This switching map shows an operating region of the internal combustion engine 1 by indicating the engine speed NE along the horizontal axis and the load along the vertical axis.
Here, the term “load” denotes an internal combustion engine torque, load rate, accelerator opening AA, or other index correlating to the load on the internal combustion engine 1. The ECU 60 can calculate the value of the load in accordance with outputs generated from the accelerator opening sensor 24, air flow meter 26, and the like. Further, the ECU 60 can calculate the engine speed NE in accordance with an output generated from the crank angle sensor 6. In this manner, the ECU 60 can determine the current operating state of the internal combustion engine 1 with reference to the switching map.
In FIG. 6, a switching pin operating line P represents a boundary for switching between the dual and single valve variable control modes. Two circles positioned side by side represent the first and second intake valves 14L, 14R, and the words within the circles indicate whether the valve opening amount is large or small.
As shown in FIG. 6, a region that is lower in engine speed and lower in load than the switching pin operating line P is a region of the single valve variable control mode. In the present embodiment, this region is referred to as the “single valve small lift region.” The single valve small lift region provides a coupled state in which the switching pin 74 of the arm coupling mechanism 72 is inserted into the pin hole 76.
On the other hand, a region that is higher in engine speed and higher in load than the switching pin operating line P is a region of the dual valve variable control mode. In the present embodiment, this region is referred to as the “dual valve great lift region.” The dual valve great lift region provides an uncoupled state in which the switching pin 74 of the arm coupling mechanism 72 is extracted from the pin hole 76.
The ECU 60 usually switches between the single and dual valve variable control modes in accordance with the switching map described above. In general, unstable, incomplete combustion is likely to result in a low engine speed/low load region. However, the present embodiment can create a swirl for combustion improvement by providing the second intake valve 14R with a great lift and the first intake valve 14L with a small lift in the single valve small lift region, which corresponds to a low engine speed/low load region. This makes it possible to reduce fuel consumption and exhaust emissions. In the dual valve great lift region, which corresponds to a high engine speed/high load region, on the other hand, the present embodiment can introduce an adequate amount of air into the cylinder by providing both intake valves 14 with a great lift.
When the operating state of the internal combustion engine 1 changes from the single valve small lift region to the dual valve great lift region, the ECU 60 usually switches to the dual valve variable control mode by extracting the switching pin 74 from the pin hole 76 without delay. However, it is conceivable that the ECU 60 may revert to the single valve small lift region within a short period of time depending on the situation even when the operating state changes from the single valve small lift region to the dual valve great lift region.
The above situation may occur when, for instance, the vehicle accelerates after it has started moving. Before the vehicle starts moving, the internal combustion engine 1 is idling as indicated by point A in FIG. 6. As the vehicle accelerates after starting in first gear, the operating state changes from point A to point B in FIG. 6 and then from point B to point C. Subsequently, an accelerator pedal is released with a clutch disengaged to shift up to second gear. Since this causes the internal combustion engine 1 to revert to an idling state, the operating state changes from point C to point A.
Shifting up to third gear and then fourth gear brings about the same changes as described above. In other words, when the vehicle accelerates after it has started moving, the operating state of the internal combustion engine 1 changes from point A through point B, point C and then back to point A in FIG. 6 within a relatively short period of time. If, in such an instance, the arm coupling mechanism 72 immediately performs a switching operation in accordance with the switching map shown in FIG. 6, the switching pin 74 is extracted from the pin hole 76 when the operating state changes from point B to point C, and then inserted back into the pin hole 76 when the operating state changes from point C to point A. It means that the dual valve variable control mode is maintained for an extremely short period of time when the operating state changes from point B through point C to point A. Therefore, switching to the dual valve variable control mode does not constitute a considerable advantage. Instead, such switching constitutes a significant disadvantage. More specifically, frequent insertion/extraction of the switching pin 74 may cause premature wear and scratching of the switching pin 74 and pin hole 76. Consequently, the present embodiment does not perform a switching operation for the switching pin 74 in the above situation in consideration of durability of the arm coupling mechanism 72.
The above switching operation, which should be avoided, takes place due to gear shifting by the transmission. Therefore, the present embodiment identifies and avoids a gear-shift-induced switching operation by temporarily disabling the switching operation of the arm coupling mechanism 72 during a predetermined period of time after a gear shift by the transmission.
When the above process is performed, a switching operation that is not absolutely necessary can be identified and avoided not only when the vehicle accelerates after the start of moving but also in the following situation. Points D to K in FIG. 7 indicate operating state changes that occur when the vehicle begins to climb a hill during high-speed running. In this situation, the operating state of the internal combustion engine 1 changes as described below. When the vehicle begins to run uphill, the vehicle velocity gradually decreases due to grade resistance, thereby gradually decreasing the engine speed NE (point D to point E). A driver of the vehicle then shifts down for the purpose of recovering the previous speed. When the accelerator pedal is released with the clutch disengaged for downshifting, the internal combustion engine 1 changes toward an idle state (point E to point F). As the accelerator pedal is depressed after downshifting, the internal combustion engine 1 changes toward a high engine speed/high load state (point F to point G). As acceleration continues, the engine speed NE increases (point G to point H). When the vehicle velocity is adequately recovered, the driver shifts up. When the accelerator pedal is released with the clutch disengaged for upshifting, the internal combustion engine 1 changes toward an idle state (point H to point I). After upshifting, the engine speed NE drops below a level prevailing before upshifting (point I to point J). A steady operation then takes place in the newly selected gear (point J to point K).
If, in the above situation, the arm coupling mechanism 72 immediately performs a switching operation in accordance with the switching map shown in FIG. 7, the switching pin 74 is extracted from the pin hole 76 when the operating state changes from point F to point G, and after a short time, the switching pin 74 is inserted back into the pin hole 76 when the operating state changes from point H to point I. In this case, too, the dual valve variable control mode persists for an extremely short period of time. Therefore, switching to the dual valve variable control mode does not constitute a considerable advantage. Instead, such switching constitutes a significant disadvantage because it may cause premature wear of the switching pin 74 and pin hole 76. It means that the switching operation in the above case should also be avoided. The present embodiment can refrain from performing the above switching operation, which should be avoided, by detecting the execution of a gear shift at point F and temporarily disabling the switching operation of the arm coupling mechanism 72 for a predetermined period of time after detection.

Details of Process Performed by First Embodiment

FIG. 8 is a flowchart illustrating a routine that the ECU 60 according to the present embodiment executes to implement the above functionality. It is assumed that this routine is periodically executed at predetermined time intervals. First of all, the routine shown in FIG. 8 performs step 100 to judge whether a gear shift is performed by the transmission. The shift position sensor 62 detects whether a gear shift is performed. If the judgment result obtained in step 100 indicates that no gear shift is performed, the routine does not perform the following processing steps because it is not necessary to disable the switching operation of the arm coupling mechanism 72. In this instance, normal control is continuously exercised so as to immediately switch between the single and dual valve variable control modes in accordance with the switching map.
If, on the other hand, the judgment result obtained in step 100 indicates that a gear shift is performed, step 102 is followed to judge whether the operating state of the internal combustion engine 1 has changed from the single valve small lift region to the dual valve great lift region within a predetermined period of time after the gear shift. The predetermined period of time is based, for instance, on data obtained by examining the time required for a change from point B through point C to point A in FIG. 6 and a change from point F through point G, point H to point I in FIG. 7, and stored in the ECU 60.
If the judgment result obtained in step 102 does not indicate a change from the single valve small lift region to the dual valve great lift region, it means that the arm coupling mechanism 72 is not instructed to perform a switching operation. In this instance, it is not necessary to disable the switching operation; therefore, the routine continuously exercises normal control without performing the following processing steps.
If, on the other hand, the judgment result obtained in step 102 indicates a change from the single valve small lift region to the dual valve great lift region, step 104 is performed to disable the switching operation of the arm coupling mechanism 72. In other words, the routine refrains from switching to the dual valve variable control mode with the switching pin 74 left inserted in the pin hole 76 although the operating state of the internal combustion engine 1 has switched to the dual valve great lift region. When a change from the single valve small region to the dual valve great lift region is found in step 102, it corresponds to a change from point B to point C in FIG. 6 or a change from point F to point G in FIG. 7, and it is anticipated that the operating state may revert to the single valve small lift region within a short period of time. Step 104, which is mentioned above, is performed to avoid a switching operation in such an instance.
Next, the routine shown in FIG. 8 performs step 106 to judge whether a predetermined period of time is reached by the elapsed time since an operating state change from the single valve small region to the dual valve great lift region. The present embodiment performs step 104 to avoid a switch to the dual valve variable control mode because it anticipates that the operating state will revert to the single valve small lift region within a short period of time. However, the operating state may remain in the dual valve great lift region without immediately reverting to the single valve small lift region depending on vehicle driving conditions and operations performed by the driver. In such an instance, a switch to the dual valve variable control mode should be made to let the internal combustion engine 1 deliver its expected performance. Therefore, if the operating state does not revert to the single valve small lift region when the predetermined period of time is reached by the elapsed time since a change to the dual valve great lift region in step 106, the present embodiment terminates the process of the routine (RETURN) and resumes normal control. When normal control resumes, a switch to the dual valve variable control mode is made in accordance with the switching map. It is assumed that the predetermined period of time usually ranges from several seconds to ten-odd seconds although its ideal value varies, for instance, with the type of the internal combustion engine 1 and the use of the vehicle in which the internal combustion engine 1 is mounted.
Next, the routine shown in FIG. 8 performs step 108 to judge whether the operating state has changed to a region other than the single valve small lift region and dual valve great lift region. The region other than the single valve small lift region and dual valve great lift region is a dual valve variable lift region. In the dual valve variable lift region, control is exercised in the dual valve variable control mode so that the lift amounts of both intake valves 14 vary between a medium lift and a small lift. The dual valve variable lift region is set for the purpose, for instance, of enhancing the effect of engine braking when the internal combustion engine 1 decelerates. The range of the dual valve variable lift region is stored in the ECU 60 separately from the switching map.
If it is found in step 108 that the operating state is changed to the dual valve variable lift region, the routine terminates (RETURN) to resume normal control. When normal control resumes, a switch to the dual valve variable control mode is made in accordance with predetermined rules. The dual valve variable lift region can be set as needed, for instance, for low-load driving, idling, low-temperature startup, and a cold climate as well as for deceleration.
Next, the routine shown in FIG. 8 performs step 110 to judge whether the operating state has changed back from the dual valve great lift region to the single valve small lift region. In this instance, a switch to the dual valve variable control mode is prohibited by the process performed in step 104 above. If the operating state reverts to the single valve small lift region in this instance, no instruction is issued for switching to the dual valve variable control mode; therefore, there is no need to disable the switching operation. In this situation, therefore, the routine terminates (RETURN) to resume normal control. If the operating state remains in the dual valve great lift region in step 110 above, the routine repeats steps 106 and beyond.
If the switching operation of the arm coupling mechanism 72 is not absolutely necessary, the process described above disables such a switching operation. This makes it possible to avoid undue wear of the arm coupling mechanism 72 and enhance its durability.
The first embodiment, which has been described above, assumes that the shift position sensor 62 detects a gear shift by the transmission. However, an alternative gear shift detection method may be used. For example, a clutch sensor for detecting clutch engagement/disengagement may be used to detect a gear shift upon clutch disengagement (in a situation where a manual transmission is used). Another alternative would be to detect a gear shift in accordance with the ratio between the engine speed NE and vehicle velocity. Since a vehicle velocity sensor is generally installed in any vehicle, the use of a method based on vehicle velocity makes it possible to detect a gear shift without adding a new sensor.
The first embodiment, which has been described above, disables the switching operation in a situation where the operating state has changed from the single valve small lift region to the dual valve great lift region under predefined conditions. However, the present invention may alternatively disable the switching operation in a situation where the operating state has conversely changed from the dual valve great lift region to the single valve small lift region.
The first embodiment, which has been described above, uses a valve mechanism that continuously varies the valve opening amounts of the first and second intake valves 14L, 14R (in the dual valve variable control mode) or the valve opening amount of the first intake valve 14L (in the single valve variable control mode). However, the present invention may alternatively use a valve mechanism that varies the above-mentioned valve opening amounts in multiple steps.
The first embodiment, which has been described above, assumes that the present invention is applied to a variable valve operating apparatus for an intake valve. However, the present invention can also be applied to a variable valve operating apparatus for an exhaust valve.
The above modifications can also be applied to the other embodiments, which will be described later.
In the first embodiment, which has been described above, the single valve small lift region corresponds to the “single valve variable control region” according to the first aspect of the present invention; the dual valve great lift region corresponds to the “dual valve variable control region” according to the first aspect of the present invention; the arm coupling mechanism 72 corresponds to the “switching mechanism” according to the first aspect of the present invention; and the ECU 60 corresponds to the “storage means” according to the first aspect of the present invention. The “normal control means” according to the first aspect of the present invention is implemented when the ECU 60 causes the arm coupling mechanism 72 to perform a switching operation in accordance with the switching map; the “condition judgment means” according to the first aspect of the present invention is implemented when the ECU 60 performs steps 100 and 102; the “disable means” according to the first aspect of the present invention is implemented when the ECU 60 performs step 104; and the “enable means” according to the fourth aspect of the present invention is implemented when the ECU 60 performs step 106.

Second Embodiment

Features of Second Embodiment

A second embodiment of the present invention will now be described with reference to FIG. 9. However, the differences between the foregoing embodiment and the second embodiment will be mainly described while skipping the description of features common to these two embodiments or describing such features briefly. The system according to the second embodiment can be implemented by using the same hardware configuration as the first embodiment and allowing the ECU 60 to execute a routine shown in FIG. 9, which will be described later.
While the vehicle is stopped, the driver may step on the accelerator pedal to let the internal combustion engine 1 perform a free acceleration (so-called racing) operation. This free acceleration operation is rarely conducted for an extended period of time. Therefore, even if the operating state changes from the single valve small lift region to the dual valve great lift region during a free acceleration operation, it is anticipated that the operating state will revert to the single valve small lift region within a short period time. In view of such circumstances, the present embodiment also refrains from switching to the dual valve variable control mode in the above instance in order to enhance the durability of the arm coupling mechanism 72.

Details of Process Performed by Second Embodiment

FIG. 9 is a flowchart illustrating a routine that the ECU 60 according to the present embodiment executes to implement the above functionality. First of all, the routine shown in FIG. 9 performs step 120 to judge in accordance with an output generated from the shift position sensor 62 whether the transmission is shifted to neutral (when a manual or automatic transmission is used) or shifted to park (when an automatic transmission is used). If the transmission is not shifted to neutral or park, the routine does not perform the following processing steps because a free acceleration operation does not take place.
If it is found in step 120 that the transmission is shifted to neutral or park, the routine performs step 122 to judge whether the operating state of the internal combustion engine 1 has changed from the single valve small lift region to the dual valve great lift region. If the judgment result obtained in step 122 indicates a change to the dual valve great lift region, it can be concluded that a free acceleration operation is being conducted. In this instance, therefore, step 124 is performed to disable the switching operation of the arm coupling mechanism 72. More specifically, although the operating state of the internal combustion engine 1 is changed to the dual valve great lift region, the switching pin 74 is left inserted in the pin hole 76 to refrain from switching to the dual valve variable control mode.
Next, the routine shown in FIG. 9 performs step 126 to judge whether the operating state has changed to a region other than the dual valve great lift region, that is, to the single valve small lift region or dual valve variable lift region. If the obtained judgment result indicates a change to a region other than the dual valve great lift region, it can be concluded that the free acceleration operation is terminated. Therefore, the routine terminates to resume normal control (RETURN). If, on the other hand, the obtained judgment result does not indicate a change to a region other than the dual valve great lift region, it can be concluded that the free acceleration operation is still being conducted. In this instance, the routine returns to step 124 and keeps the switching operation disabled.
When the above process is performed, it is possible to prevent the arm coupling mechanism 72 from performing an extra switching operation during a free acceleration operation and enhance the durability of the arm coupling mechanism 72.

Third Embodiment

Features of Third Embodiment

A third embodiment of the present invention will now be described with reference to FIG. 10. However, the differences between the foregoing embodiments and the third embodiment will be mainly described while skipping the description of features common to these three embodiments or describing such features briefly. The third embodiment has the same hardware configuration as the first embodiment. The system according to the third embodiment can be implemented by allowing the ECU 60 to execute a routine shown in FIG. 10, which will be described later, in addition to the process according to the first or second embodiment.
As mentioned earlier, the arm coupling mechanism 72 moves the switching pin 74 by using the hydraulic pressure of the lubricating oil for the internal combustion engine 1. While the internal combustion engine 1 operates, sludge (viscous material) may be produced in the lubricating oil. If by any chance the switching pin 74 does not operate for an extended period of time while the sludge is deposited around the switching pin 74, the switching pin 74 may bind in the hydraulic chamber 75 or pin hole 76 and become inoperative.
As described earlier, the first and second embodiments disable the switching operation of the arm coupling mechanism 72 in a predefined situation. This reduces the frequency with which the arm coupling mechanism 72 performs the switching operation. When the frequency of the switching operation of the arm coupling mechanism 72 decreases, the switching pin 74 is likely to stay put for an extended period of time. As a result, it is highly probable that the switching pin 74 may bind due to the sludge.
Therefore, if a predetermined value is exceeded by the number of times the switching operation of the arm coupling mechanism 72 was disabled or the cumulative time during which the switching operation of the arm coupling mechanism 72 was disabled, the present embodiment enables the switching operation to prevent the switching pin 74 from binding.

Details of Process Performed by Third Embodiment

FIG. 10 is a flowchart illustrating a routine that the ECU 60 according to the present embodiment executes to implement the above functionality. The routine shown in FIG. 10 is executed in conjunction with the routine shown in FIG. 8 or 9.
The routine shown in FIG. 10 performs step 130 to measure the number of times the switching operation of the arm coupling mechanism 72 was disabled by the routine shown in FIG. 8 or 9 and the cumulative time during which the switching operation of the arm coupling mechanism 72 was disabled by the routine shown in FIG. 8 or 9, and store the measured number of times and cumulative time in the ECU 60. The routine then performs step 132 to judge whether predetermined values are exceeded respectively by the number of times or cumulative time. The predetermined values are based on the characteristics of the internal combustion engine 1 and the vehicle in which the internal combustion engine 1 is mounted, and stored in the ECU 60. These values are predetermined so as to ensure that the switching operation is performed before the switching pin 74 binds.
If the judgment result obtained in step 132 indicates that one of the predetermined values is exceeded by the measured number of times or cumulative time, step 134 is performed to stop the routine's control for disabling the switching operation, which is shown in FIG. 8 or 9, and resumes normal control. While normal control is exercised, the arm coupling mechanism 72 performs its switching operation in accordance with the switching map.
Next, step 136 is performed to judge whether the switching operation has been performed by the arm coupling mechanism 72 under normal control. If the switching operation has been actually performed by the arm coupling mechanism 72, it means that the switching operation has been performed to prevent the switching pin 74 from binding. In this instance, step 138 is performed to lift the ban on switching operation disable control by the routine shown in FIG. 8 or 9 and enable a switching operation disable control function. The measured number of times and cumulative time, which were stored in step 130, are then reset to zero (0). In the above process, whether the switching operation disable control function should be enabled is determined by checking whether the switching operation is actually performed by the arm coupling mechanism 72. However, an alternative determination method may be used. For example, whether the switching operation disable control function should be enabled may alternatively be determined by checking whether the arm coupling mechanism 72 is instructed to perform a switching operation.
When the above process is performed, it is possible to properly prevent the switching pin 74 from binding due to a decrease in the frequency with which the arm coupling mechanism 72 performs a switching operation during the process according to the first or second embodiment.
In the third embodiment, which has been described above, the “measurement means” according to the fifth aspect of the present invention is implemented when the ECU 60 performs step 130; and the “permission means” according to the fifth aspect of the present invention is implemented when the ECU 60 performs steps 132 and 134.

Fourth Embodiment

Features of Fourth Embodiment

A fourth embodiment of the present invention will now be described with reference to FIG. 11. However, the differences between the foregoing embodiments and the fourth embodiment will be mainly described while skipping the description of features common to these four embodiments or describing such features briefly. The fourth embodiment has the same hardware configuration as the first embodiment. Further, the fourth embodiment performs basically the same process as the first or second embodiment.
FIG. 11 shows valve lift curves of the first intake valve 14L and the second intake valve 14R. The present embodiment assumes that the valve lift of the first intake valve 14L is substantially equal to that of the second intake valve 14R in the dual valve variable control mode. FIG. 11 shows valve lifts A to E, which are described below.
Valve lift A is the maximum valve lift in the dual valve great lift region (dual valve variable control mode). This valve lift is preset in accordance with maximum power requirements for the internal combustion engine 1.
Valve lift B prevails in a state where the rotational position of the control shaft 41 coincides with the pin switching position, that is, the switching pin 74 aligns with the pin hole 76. More specifically, valve lift B prevails while the great lift arm 71 is not coupled to the second swing cam arm 50R.
Valve lift C prevails in a state where the great lift arm 71 is coupled to the second swing cam arm 50R so that the valve opening amount of the second intake valve 14R remains large. More specifically, valve lift C is the valve lift of the second intake valve 14R in the single valve variable control mode.
Valve lift D is the minimum valve lift that can be set by the variable valve mechanism 40. Valve lift E is the maximum valve lift that can be set by the variable valve mechanism 40. In the present embodiment, valve lift A represents the upper limit of its operating range; therefore, valve lift E is not actually used.
In the single valve small lift region, a target valve lift is set within a range from valve lift D to valve lift B. In other words, the target position of the control shaft 41 in the single valve small lift region is within a range that begins at the pin switching position and extends toward a smaller lift, smaller operating angle region. In the dual valve great lift region, on the other hand, the target valve lift is set within a range from valve lift B to valve lift A. In other words, the target position of the control shaft 41 in the dual valve great lift region is within a range from the pin switching position corresponding to valve lift B to a position corresponding to valve lift A, which is in a greater lift, greater operating angle region.
As described above, the upper limit of the target valve lift in the single valve small lift region is represented by valve lift B. While normal control is exercised, the single valve variable control mode, that is, a state where the great lift arm 71 is coupled to the second swing cam arm 50R, is implemented in the single valve small lift region. Therefore, when the valve mechanism 18 is in the single valve variable control mode, control is generally exercised while the range below valve lift B is defined as the target valve lift.
Meanwhile, the first and second embodiments may disable the function for switching from the single valve variable control mode to the dual valve variable control mode and stay in the single valve variable control mode as described earlier even when the operating state has changed from the single valve small lift region to the dual valve great lift region (step 104 in FIG. 8 or step 124 in FIG. 9). Therefore, a target valve lift greater than valve lift B may be set while the valve mechanism 18 is in the single valve variable control mode. In this instance, the following situation occurs.
In the single valve variable control mode, the second intake cam 17 usually drives the great lift arm 71, which then drives the second swing cam arm 50R via the switching pin 74, as described earlier. However, if the control shaft 41 rotates beyond the pin switching position corresponding to valve lift B and toward a great lift and large operating angle region in the single valve variable control mode, the range over which the first intake cam 16 swings the second swing cam arm 50R becomes larger than the range over which the second intake cam 17 swings the second swing cam arm 50R. This causes the second swing cam arm 50R to reversely drive the great lift arm 71 via the switching pin 74. In this instance, therefore, the input roller 73 for the great lift arm 71 leaves the second intake cam 17.
If the engine speed NE and load suddenly decrease in a situation where the input roller 73 for the great lift arm 71 is separated from the second intake cam 17 as described above, the control shaft 41 instantaneously rotates toward a small lift and small operating angle region. The input roller 73 for the great lift arm 71 may then come into contact again (collide) with the second intake cam 17, thereby generating noise or damaging the surfaces of the input roller 73 and the second intake cam 17.
To avoid the above problem, the present embodiment limits the target valve lift to valve lift B or smaller when a switch from the single valve variable control mode to the dual valve variable control mode is prohibited (step 104 in FIG. 8 or step 124 in FIG. 9), that is, when the operating state enters the dual valve great lift region in the single valve variable control mode. This prevents the control shaft 41 from rotating beyond the pin switching position corresponding to valve lift B and toward a great lift and large operating angle region while the valve mechanism 18 is in the single valve variable control mode. This makes it possible to properly prevent the input roller 73 for the great lift arm 71 from leaving the second intake cam 17. Consequently, the present embodiment can absolutely avoid noise generation and prevent the surfaces of the input roller 73 and the second intake cam 17 from being damaged.
In the present embodiment, the initial target valve lift in the dual valve great lift region is within a range from valve lift B to valve lift A as described earlier. Therefore, if the target valve lift is limited to valve lift B or smaller in a situation where a switch from the single valve variable control mode to the dual valve variable control mode is prohibited, the actual target valve lift is fixed at valve lift B.
Since the present embodiment is the same as the first and second embodiment except as described above, its further description is omitted here.
In the fourth embodiment, which has been described above, the “valve opening amount limitation means” according to the sixth and seventh aspects of the present invention is implemented when the ECU 60 limits the target valve lift (target valve opening amount) to valve lift B or smaller in a situation where a switch from the single valve variable control mode to the dual valve variable control mode is prohibited (step 104 in FIG. 8 or step 124 in FIG. 9). Further, the first intake valve 16 corresponds to the “main cam” according to the seventh aspect of the present invention; the second intake valve 17 corresponds to the “sub-cam” according to the seventh aspect of the present invention; and the input roller 73 for the great lift arm 71 corresponds to the “mating member” according to the seventh aspect of the present invention.

Claims

1-7. (canceled)

8. A variable valve operating apparatus comprising:

a valve mechanism having a switching mechanism for switching between a dual valve variable control mode in which the valve opening amounts of a first valve and a second valve, which are provided for the same cylinder and of the same type, are varied continuously or in multiple steps and a single valve variable control mode in which the valve opening amount of the first valve is varied continuously or in multiple steps with the valve opening amount of the second valve fixed;

storage means for storing rules for dividing an operating region of an internal combustion engine into a dual valve variable control region, for which the dual valve variable control mode should be selected, and a single valve variable control region, for which the single valve variable control mode should be selected;

normal control means for causing the switching mechanism to perform a switching operation in accordance with the rules; and

disable means which, when the operating state of the internal combustion engine is changed from the dual valve variable control region to the single valve variable control region or vice versa within a predetermined period of time after a gear shift by a transmission positioned between the internal combustion engine and vehicle driving wheels, avoids the switching operation by disabling the switching operation in anticipation that the operating state will revert to the previous region within a short period of time.

9. A variable valve operating apparatus comprising:

normal control means for causing the switching mechanism to perform a switching operation in accordance with the rules;

condition judgment means for judging, when the operating state of the internal combustion engine switches from the dual valve variable control region to the single valve variable control region or vice versa, whether a predefined condition is established for anticipating that the operating state will revert to the previous region within a short period of time;

disable means for disabling the switching operation when the predefined condition is established; and

enable means which, if the operating state of the internal combustion engine does not revert to a previous region within a predetermined period of time after a switch from the dual valve variable control region to the single valve variable control region or vice versa, enables the switching operation no matter whether the predefined condition is established.

10. A variable valve operating apparatus comprising:

disable means for disabling the switching operation when the predefined condition is established;

measurement means for measuring the number of times the switching operation was disabled or the cumulative time during which the switching operation was disabled; and

permission means which, when a predetermined value is exceeded by the number of times the switching operation was disabled or the cumulative time during which the switching operation was disabled, permits the switching mechanism to perform a switching operation no matter whether the predefined condition is established.

11. A variable valve operating apparatus comprising:

valve opening amount limitation means for limiting a target valve opening amount when the switching operation is disabled by the disable means.

12. A variable valve operating apparatus comprising:

a storage device for storing rules for dividing an operating region of an internal combustion engine into a dual valve variable control region, for which the dual valve variable control mode should be selected, and a single valve variable control region, for which the single valve variable control mode should be selected;

a normal control device for causing the switching mechanism to perform a switching operation in accordance with the rules; and

a disable device which, when the operating state of the internal combustion engine is changed from the dual valve variable control region to the single valve variable control region or vice versa within a predetermined period of time after a gear shift by a transmission positioned between the internal combustion engine and vehicle driving wheels, avoids the switching operation by disabling the switching operation in anticipation that the operating state will revert to the previous region within a short period of time.

13. A variable valve operating apparatus comprising:

a normal control device for causing the switching mechanism to perform a switching operation in accordance with the rules;

a condition judgment device for judging, when the operating state of the internal combustion engine switches from the dual valve variable control region to the single valve variable control region or vice versa, whether a predefined condition is established for anticipating that the operating state will revert to the previous region within a short period of time;

a disable device for disabling the switching operation when the predefined condition is established; and

an enable device which, if the operating state of the internal combustion engine does not revert to a previous region within a predetermined period of time after a switch from the dual valve variable control region to the single valve variable control region or vice versa, enables the switching operation no matter whether the predefined condition is established.

14. A variable valve operating apparatus comprising:

a disable device for disabling the switching operation when the predefined condition is established;

a measurement device for measuring the number of times the switching operation was disabled or the cumulative time during which the switching operation was disabled; and

a permission device which, when a predetermined value is exceeded by the number of times the switching operation was disabled or the cumulative time during which the switching operation was disabled, permits the switching mechanism to perform a switching operation no matter whether the predefined condition is established.

15. A variable valve operating apparatus comprising:

a valve opening amount limitation device for limiting a target valve opening amount when the switching operation is disabled by the disable device.