US20100242878A1

US20100242878A1 - Variable valve apparatus for internal combustion engine

Info

Publication number: US20100242878A1
Application number: US12/814,139
Authority: US
Inventors: Masahiro Maekawa
Original assignee: Mitsubishi Fuso Truck and Bus Corp
Current assignee: Mitsubishi Fuso Truck and Bus Corp
Priority date: 2007-12-27
Filing date: 2010-06-11
Publication date: 2010-09-30
Also published as: DE112008003534T5; JP2009174319A; JP5331343B2

Abstract

In order to simultaneously exert a plurality of functions such as execution of internal EGR, application of engine braking, improvement in fuel consumption and purification of exhaust gas, a variable valve apparatus for an internal combustion engine of the invention includes a cam shaft arranged to be rotatable on a cylinder head of the internal combustion engine, a rocker shaft arranged to be capable of oscillation in the internal combustion engine, a continuous variable rocker arm mechanism which is driven by a cam formed on the cam shaft, opens or closes air intake valves and exhaust valves, and continuously makes a lift of the valves variable, and a switching rocker arm mechanism which is driven by the cam formed on the cam shaft, opens or closes the air intake valves and the exhaust valves, and switches the lift of the valves in a stepwise manner.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation application of PCT Application No. PCT/JP2008/073635, filed Dec. 25, 2008, which was published under PCT Article 21(2) in Japanese.
This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2007-338360, filed Dec. 27, 2007; and No. 2008-004745, filed Jan. 11, 2008, the entire contents of both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a variable valve apparatus for an internal combustion engine which makes it possible to change drive phases and valve lifts of an air intake valve, an exhaust valve, and the like. 2. Description of the Related Art
In an internal combustion engine such as an automobile engine, a variable valve apparatus is known which changes drive phases and lifts of intake/exhaust valves depending on driving states of the internal combustion engine to purify an exhaust gas discharged from the engine or to reduce a fuel consumption of the automobile.
As the variable valve apparatus, a variable valve apparatus having a continuous variable rocker arm mechanism is known in which a third arm is arranged between a first arm which drives a valve and a second arm caused to oscillate by a cam, the valve is driven through the third arm, and a fulcrum of oscillation of the second arm is displaced to continuously change the phase and lift of the valve (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2004-339079).
The variable valve apparatus having the continuous variable rocker arm mechanism adjusts the lift and phase of a valve to purify an exhaust gas and adjusts an opening valve angle to make it possible to improve a fuel consumption.
On the other hand, a variable valve apparatus having a switching rocker arm mechanism is known in which a mechanism which selectively transmits displacement is arranged between the first arm which drives the valve and the second arm caused to oscillate by the cam to operate or stop the first arm (for example, see Jpn. Pat. Appin. KOKAI Publication No. 2005-105953).
The variable valve apparatus having the switching rocker arm mechanism performs internal EGR by opening an exhaust valve in an intake stroke to make it possible to purify an exhaust gas and opens the exhaust valve at a compression top dead center to make it possible to apply the engine braking.

BRIEF SUMMARY OF THE INVENTION

However, the variable valve apparatus as described above must select any one of a switching rocker arm mechanism 40 and a continuous variable rocker arm mechanism 50, and can exert only one of the functions of the mechanisms. Furthermore, although the switching rocker arm mechanism 40 can be instantaneously operated, the switching rocker arm mechanism 40 cannot be finely adjusted in lift and phase of the valve. On the other hand, although the continuous variable rocker arm mechanism 50 can be finely adjusted in lift and phase, the continuous variable rocker arm mechanism 50 requires about one second for an operation and has poor responsiveness.
Therefore, it is an object of the present invention to provide a variable valve apparatus for an internal combustion engine which can execute internal EGR and apply engine braking and can simultaneously exert a plurality of functions such as improvement in fuel consumption and purification of an exhaust gas.
In order to solve the problem and achieve the object, the variable valve apparatus for an internal combustion engine of the present invention has the following configuration.
A variable valve apparatus for an internal combustion engine, comprises a cam shaft arranged to be rotatable on a cylinder head of the internal combustion engine; a rocker shaft arranged to be capable of oscillation in the internal combustion engine; a continuous variable rocker arm mechanism which is driven by a cam formed on the cam shaft, opens or closes at least one of an air intake valve and an exhaust valve, and continuously makes a lift of the valve variable; and a switching rocker arm mechanism which is driven by the cam formed on the cam shaft, opens or closes at least one of the air intake valve and the exhaust valve, and switches the lift of the valve in a stepwise manner.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a plan view showing a main part of a cylinder block in which a variable valve apparatus according to the present invention is incorporated.

FIG. 2 is a sectional view showing the cylinder head block cut along line A-A in FIG. 1 when viewed in a direction given by an arrow.

FIG. 3 is a sectional view showing the cylinder head block cut along line B-B in FIG. 1 when viewed in a direction given by an arrow.

FIG. 4 is a perspective view showing the variable valve apparatus.

FIG. 5 is an exploded perspective view showing the variable valve apparatus.

FIG. 6 is an explanatory diagram showing a control concept in execution of internal EGR.

FIG. 7 is an explanatory diagram showing a control concept in execution of internal EGR.

FIG. 8 is a sectional view showing an operation of a switching rocker arm mechanism in a normal operation.

FIG. 9 is a sectional view showing an operation of a continuous variable rocker arm mechanism in a normal operation.

FIG. 10 is a sectional view showing an operation of the switching rocker arm mechanism in execution of internal EGR.

FIG. 11 is a sectional view showing an operation of the continuous variable rocker arm mechanism in execution of internal EGR.

FIG. 12 is an explanatory diagram showing a control concept in application of engine braking.

FIG. 13 is an explanatory diagram showing a control concept in application of engine braking.

FIG. 14 is a sectional view showing an operation of the switching rocker arm mechanism in application of engine braking.

FIG. 15 is a sectional view showing an operation of the continuous variable rocker arm mechanism in application of engine braking.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a plan view showing a main part of a cylinder head 10 in which a variable valve apparatus 20 for an internal combustion engine according to a first embodiment of the invention is incorporated, FIG. 2 is a sectional view showing the cylinder head 10 cut along line A-A in FIG. 1 when viewed in a direction given by an arrow, FIG. 3 is a sectional view showing the cylinder head 10 cut along line B-B in FIG. 1 when viewed in a direction given by an arrow, FIG. 4 is a perspective view showing the variable valve apparatus 20, and FIG. 5 is an exploded perspective view showing the variable valve apparatus 20.
As shown in FIGS. 1 to 3, one pair of air intake valves 12 and 13 and one pair of exhaust valves 14 and 15 are arranged on the cylinder head 10. The air intake valves 12 and 13 are arranged in an intake path 10 a of the cylinder head 10 such that the air intake valves 12 and 13 can be reciprocated in an axial direction, and the air intake valves 12 and 13 are always biased in such a direction that the intake path 10 a is closed by valve springs 12 a and 13 a. The exhaust valves 14 and 15 are arranged in an exhaust path 10 b of the cylinder head 10 such that the exhaust valves 14 and 15 can be reciprocated in the axial direction, and the exhaust valves 14 and 15 are always biased in such a direction the intake path 10 a is closed by valve springs 14 a and 15 a. The cylinder 11 is attached to a cylinder block (not shown) located below the cylinder head 10.
The variable valve apparatus 20 is a valve operation apparatus which opens/closes valves of an internal combustion engine. One pair of variable valve apparatuses 20 is arranged to sandwich the cylinder 11. Since the one pair of variable valve apparatuses 20 has a structure symmetrical with reference to the cylinder 11, only the variable valve apparatus 20 on the exhaust valves 14 and 15 side will be explained, and an explanation of the variable valve apparatus 20 on the air intake valves 12 and 13 side is not explained.
The cylinder head 10 comprises one pair of cam shafts 21 arranged to be rotatable, one pair of rocker shafts 30 arranged to be capable of oscillation, one pair of switching rocker arm mechanisms 40 which are driven by a cam 22 formed on the cam shaft 21 and open and close the air intake valves 12 and 13 and the exhaust valves 14 and 15 and switch lifts of the air intake valves 12 and 13 and the exhaust valves 14 and 15 in a stepwise manner, and one pair of continuous variable rocker arm mechanisms 50 which are driven by a cam 23 formed on the cam shaft 21 and open and close the air intake valves 12 and 13 and the exhaust valves 14 and 15 and continuously make the lifts variable. The switching rocker arm mechanisms 40 and the continuous variable rocker arm mechanisms 50 share a rocker arm 60.
The cam shafts 21 and the rocker shafts 30 are connected to a crank shaft (not shown) of an internal combustion engine through a cam chain, gears, and the like. When the crank shaft is rotated, the cams 22 and 23 having different cam profiles are rotationally driven in a direction indicated by an arrow R. The cams 22 and 23 drive the variable valve apparatus 20 at a predetermined timing described later.
An oil path 31 to which engine oil is supplied is arranged inside the rocker shaft 30. An oil pressure supply mechanism 80 which supplies the engine oil to the oil path 31 is connected to the oil path 31. The rocker shaft 30 comprises a drive mechanism 90 which controls a rotational angle position about a shaft center line of the rocker shaft 30. Furthermore, a notch 32 is formed in the rocker shaft 30 at a position corresponding to the continuous variable rocker arm mechanism 50.
With reference to FIGS. 2 and 5, the switching rocker arm mechanism 40 will be explained. The switching rocker arm mechanism 40 comprises the shared rocker arm 60 supported by the rocker shafts 30 to be capable of oscillation and formed to make it possible to drive the exhaust valves 14 and 15, and a switching rocker arm 41 driven by the cam 22 and arranged to be capable of oscillation on the rocker shaft 30.
In the switching rocker arm 41, a boss portion 41 a supported by the rocker shaft 30 to be capable of oscillation is formed; a strike arm 41 b which projects upwardly from the boss portion 41 a, enters a window portion 71 b of a vertical piston structure 70 serving as a transmission mechanism described later, and retreats from the window portion 71 b is formed; and a roller 41 c capable of oscillation is formed. When the roller 41 c is brought into contact with the cam 22 to rotate the cam 22, the switching rocker arm 41 is caused to oscillate by using a shaft center line of the rocker shaft 30 as a fulcrum. A trench 41 d is formed in the switching rocker arm 41.
Reference number 42 in FIG. 5 denotes a torsion coil spring. A bent portion 42 a is formed on one end side of the spring, and a moving portion 42 b extending in an axial direction of the rocker shafts 30 and bent to the outside in the radial direction is formed on the other end side of the spring. The bent portion 42 a is inserted into the cylinder head 10. When the moving portion 42 b of the torsion coil spring 42 is engaged in the trench 41 d, the torsion coil spring 42 biases the switching rocker arm 41 such that the roller 41 c moves along the lines of the cam 22.
The shared rocker arm 60 comprises a boss portion 61 fitted in the rocker shaft 30 portion to be capable of oscillation, arms 62 and 63 extending from the boss portion 61 to the exhaust valves 14 and 15, and a pressed portion 64 pressed by a pressing portion 53 b described later. In the boss portion 61, a flow path 61 a which guides the engine oil from the oil path 31 is formed.
In the boss portion 61, as a transmission mechanism to selectively transmit displacement from the switching rocker arm 41 to the shared rocker arm 60, the cylindrical vertical piston structure 70 is arranged. The vertical piston structure 70 comprises a storage tube 71 having a hollow portion 71 a continuing to an internal surface of the boss portion 61 and the window portion 71 b on the side surface, a lid member 72 which blocks an upper-end opening of the hollow portion 71 a of the storage tube 71, a piston 73 reciprocatingly stored in the hollow portion 71 a, and a spring 74 arranged on the lid member 72 to bias the piston 73 on the boss portion 61 side. A notch 73 a is formed in the piston 73. The notch 73 a is generally set such that the notch 73 a is located at a position of the window portion 71 b by the operation of the spring 74. When oil pressure is applied by the oil pressure supply mechanism 80, engine oil is supplied from the oil path 31 to the hollow portion 71 a to compress the spring 74 and push up the piston 73. In this manner, a circumference of the piston 73 is exposed to the window portion 71 b. In contrast to this, when the oil pressure is released, the piston 73 is pushed down by the operation of the spring 74. An on/off operation of the oil pressure can be instantaneously performed.
The strike arm 41 b is arranged to face the window portion 71 b. The strike arm 41 b is formed to have a shape such that the strike arm 41 b idly moves in the notch 73 a when the notch 73 a is positioned at the window portion 71 b and moves while being struck on the circumference portion of the piston 73 when the circumference portion is positioned at the window portion 71 b.
In this manner, in the structure, when the strike arm 41 b of the switching rocker arm 41 is not struck on the piston 73, cam displacement from the switching rocker arm 41 is not transmitted to the shared rocker arm 60. When the strike arm 41 b is struck on the piston 73, the cam displacement from the switching rocker arm 41 opens the exhaust valves 14 and 15 through the shared rocker arm 60. An oil discharge chamber 32 having a width larger than that of the flow path 61 a is formed in the rocker shaft 30 on the downstream side of the oil path 31, so that the engine oil can be supplied to the hollow portion 71 a even when the position of the flow path 61 a is changed by oscillation of the rocker shaft 30 itself or oscillation of the switching rocker arm 41 with rotation of the cam 22. The width of the oil discharge chamber 32 is preferably larger than a distance of oscillation of the switching rocker arm 41 and preferably set to a width at which the engine oil can be supplied to the flow path 61 a even when the rocker shaft 30 reaches the position of maximum oscillation.
Furthermore, an oil supply chamber 75 having a width larger than that of the flow path 61 a is formed in the vertical piston structure 70 on an upstream side of the hollow portion 71 a. Even when the switching rocker arm 41 is caused to oscillate with rotation of the cam 22 to change the position of the flow path 61 a, the engine oil can be supplied to the hollow portion 71 a. The width of the oil supply chamber 75 is preferably larger than a distance of oscillation of the switching rocker arm 41.
The continuous variable rocker arm mechanism 50 will be explained with reference to FIGS. 3 and 5. The continuous variable rocker arm mechanism 50 comprises the shared rocker arm 60 supported by the rocker shaft 30 to be capable of oscillation and formed to make it possible to drive the exhaust valves 14 and 15, a continuous variable arm 53 driven by the cam 23 and arranged to be capable of oscillation about a fulcrum Q set on the rocker shaft 30 side, and an intermediate arm 51 which is arranged between the shared rocker arm 60 and the continuous variable arm 53 and transmits oscillation displacement of the continuous variable arm 53 to the shared rocker arm 60 to drive the shared rocker arm 60.
The intermediate arm 51 comprises an annular shaft fitting portion 51 a and a pressing portion 51 b projecting from the shaft fitting portion 51 a in a radial direction. A roller 51 c is arranged on the pressing portion 51 b. When the intermediate arm 51 is caused to oscillate about the rocker shaft 30, the pressing portion 53 b presses the pressed portion 64 of the shared rocker arm 60, and the shared rocker arm 60 opens the exhaust valves 14 and 15.
The continuous variable arm 53 comprises a connection member 54 which connects the continuous variable arm 53 and the rocker shaft 30. The connection member 54 is a stud bolt, has a spherical universal coupling 54 a on one end side thereof, is screwed into a screw hole 33 formed in the notch 32 of the rocker shaft 30, and is fixed by a lock nut 54 b. When the connection member 54 is fixed to the rocker shaft 30, the universal coupling 54 a functions as the fulcrum Q.
Reference number 55 in FIG. 5 denotes a torsion coil spring. The torsion coil spring 55 has a bent portion 55 a formed on one end side thereof, and a moving portion 55 b formed on the other end side thereof, extending in an axial direction of the rocker shaft 30 and bent to the outside in the radial direction. The bent portion 55 a is inserted into the cylinder head 10.
The continuous variable arm 53 is formed to have an almost laterally-facing U shape in a side view. A laterally-facing U-shaped base end 53 a is formed on a lower side in FIG. 5, and a contact portion 53 b is formed on an upper side in FIG. 5. The base end 53 a has a recessed portion 53 c formed on an upper surface thereof. The recessed portion 53 c is formed to have an almost semi-spherical shape corresponding to the spherical shape of the universal coupling 54 a and incorporated to be capable of oscillation by using the universal coupling 54 a as a fulcrum.
On the continuous variable arm 53, a roller 53 d is arranged to be capable of oscillation at an intermediate position between the base end 53 a and the contact portion 53 b. When the roller 53 d is brought into contact with the cam 23 and the cam 23 is rotated, the continuous variable arm 53 is caused to oscillate by using the center of the universal coupling 54 a as a fulcrum.
Reference number 56 in FIG. 5 denotes a transformation member. The transformation member 56 is formed to have a triangular tabular shape which is long on one end side, and a slide surface portion 56 a is formed on an upper-side surface in FIG. 5, and a transmission surface portion 56 b is arranged on a lower-side surface in FIG. 5. The slide surface portion 56 a is formed to have a curvature equal to that of a pad 57 (see FIG. 9) fixed to the cylinder head 10 and slidably moves along an arc-like lower surface of the pad 57.
The transmission surface portion 56 b is formed such that a distance between the transmission surface portion 56 b and the slide surface portion 56 a has a predetermined value along the slide surface portion 56 a . More specifically, the transmission surface portion 56 b is formed such that, when the transformation member 56 is slidably moved along an arc-like lower surface of the pad 57, a member being in contact with the transmission surface portion 56 b at a predetermined position makes a predetermined motion in a direction perpendicular to the pad 57 with the movement of the transformation member 56.
A trench 56 c is formed in the transmission surface portion 56 b, and the moving portion 55 b of the torsion coil spring 55 is engaged in the trench 56 c. When the moving portion 55 b is engaged in the trench 56 c, the torsion coil spring 55 biases the transformation member 56 such that the transformation member 56 moves to the continuous variable arm 53 side.
Furthermore, a semi-cylindrical joint 57 is arranged between the transformation member 56 and the contact portion 53 b of the continuous variable arm 53. The joint 57 is attached to the contact portion 53 b of the continuous variable arm 53 and slidably fitted on the transformation member 56. The joint 57 is designed to absorb a change in a contact angle between the transformation member 56 and the contact portion 53 b and to transmit a pressing operation of the continuous variable arm 53 to the transformation member 56.
An operation of the continuous variable rocker arm mechanism 50 will be explained with reference to FIG. 9. When a valve opening timing or a valve closing timing of the exhaust valve is to be retarded, the rocker shaft 30 is caused to oscillate by the drive mechanism 90 in such a direction that the universal coupling 54 a of the connection member 54 approaches the exhaust valves 14 and 15 with reference to a neutral position.
The base end 53 a is pulled to the left by the universal coupling 54 a, and the continuous variable arm 53 moves to the left as a whole. On the other hand, the transformation member 56 is biased by the torsion coil spring 55 on the continuous variable arm 53 side. For this reason, the transformation member 56 is brought into tight contact with the pad 57, and the roller 53 d is brought into contact with the cam 23. At this time, since the cam shafts 21 rotate counterclockwise, an angle between a start point of a cam nose and a contact point between the roller 53 d and the cam 23 is set to be widest, and the continuous variable arm 53 is driven by the cam 23 later than that in the neutral state. As a result, the valve opening timing or the valve closing timing are retarded.
On the other hand, when a valve opening or valve closing timing of an exhaust valve is to be advanced, the universal coupling 54 a of the connection member 54 is caused to oscillate in such a direction that the universal coupling 54 a goes away from the exhaust valves 14 and 15 side with reference to the neutral position.
The base end 53 a is pulled to the right by the universal coupling 54 a, and the continuous variable arm 53 moves to the right as a whole. On the other hand, the transformation member 56 is biased by the torsion coil spring 55 on the continuous variable arm 53 side. For this reason, the transformation member 56 is brought into tight contact with the pad 57, and the roller 53 d is brought into contact with the cam 23.
At this time, since the cam shafts 21 rotate counterclockwise, an angle between a start point of a cam nose and a contact point between the roller 53 d and the cam 23 is set to be narrowest, and the continuous variable arm 53 is driven by the cam 23 earlier than that in the neutral state. As a result, the valve opening timing or the valve closing timing are advanced.
The retarding and advancing adjustments are continuously performed by continuously adjusting an angle position of the rocker shaft 30.
As described above, the variable valve apparatus 20 can change a valve opening timing and a valve closing timing by making the drive mechanism 90 cause the rocker shaft 30 to oscillate. For this reason, the valve opening timing and the valve closing timing are changed to make it possible to increase an intake air flow and to achieve a reduction in fuel consumption.
With this configuration, in the internal combustion engine comprising the variable valve apparatus 20 having the switching rocker arm mechanism 40 and the continuous variable rocker arm mechanism 50, the following control can be performed.
First, the operations of the switching rocker arm mechanism 40 and the continuous variable rocker arm mechanism 50 performed when an amount of internal EGR is optimized will be explained while comparing a “normal operation” and an “internal EGR operation”. FIG. 6 is a graph showing a relationship between the phase and lift of the cam shaft 21. Reference symbol EX denotes opening valves (lifts) of the exhaust valves 14 and 15, and reference symbol IH denotes opening valves (lifts) of the air intake valves 12 and 13.

The cam shaft 21 causes an exhaust stroke which opens the exhaust valves 14 and 15 to slightly overlap an intake stroke performed by opening the air intake valves 12 and 13. An operation of the switching rocker arm mechanism 40 at this time is shown in FIG. 8, and an operation of the continuous variable rocker arm mechanism 50 at this time is shown in FIG. 9. In the normal operation, on both the air intake valves 12 and 13 side and the exhaust valves 14 and 15 side, an operation mode of the switching rocker arm mechanism 40 is set to be off, and an operation mode of the continuous variable rocker arm mechanism 50 is set to a normal (neutral) mode.
More specifically, when the operation mode of the switching rocker arm mechanism 40 is set to be off, oil pressure is not applied by the oil pressure supply mechanism 80, and engine oil is not supplied into the hollow portion 71 a in the switching rocker arm mechanism 40. For this reason, the piston 73 is biased downward by an elastic force of the spring 74, and the notch 73 a is located at the window portion 71 b. On the other hand, the roller 41 c moves along the cam 22 by the rotation of the cam 22 rotated by the cam shaft 21, and the switching rocker arm 41 oscillates about the rocker shaft 30 at predetermined intervals in a direction indicated by an arrow E in FIG. 8. However, even when the strike arm 41 b is inserted into the window portion 71 b, the strike arm 41 b is inserted into only the notch 73 a but not brought into contact with the piston 73. Therefore, motion of the switching rocker arm 41 is not transmitted to the shared rocker arm 60. Consequently, the switching rocker arm mechanism 40 does not operate, and the air intake valves 12 and 13 and the exhaust valves 14 and 15 are not driven.
In the continuous variable rocker arm mechanism 50, the rocker shaft 30 is set at a neutral position by means of the drive mechanism 90. Therefore, the roller 53 d moves along the cam 23 by rotation of the cam 23 rotated by the cam shaft 21, and the continuous variable arm 53 oscillates about the rocker shaft 30 at predetermined intervals in a direction indicated by an arrow F in FIG. 9. In this manner, motion of the continuous variable arm 53 is transmitted to the shared rocker arm 60 through the transformation member 56 and the intermediate arm 51, and the air intake valves 12 and 13 and the exhaust valves 14 and 15 are driven along a profile of the cam 23.
As described above, in the normal operation, by the continuous variable rocker arm mechanism 50, the air intake valves 12 and 13 and the exhaust valves 14 and 15 are driven according to phases and lifts which change along a solid line S.

In an internal EGR operation, on the air intake valves 12 and 13 side, the operation mode of the switching rocker arm mechanism 40 is set to be off, and the operation mode of the continuous variable rocker arm mechanism 50 is set to an early closing (advance) mode. On the exhaust valves 14 and 15 side, the operation mode of the switching rocker arm mechanism 40 is set to be on, and the operation mode of the continuous variable rocker arm mechanism 50 is set to a normal (neutral) mode.
The operations of the switching rocker arm mechanism 40 and the continuous variable rocker arm mechanism 50 are summarized as follows.

TABLE 1

Optimization of amount of internal EGR

	Switching rocker	Continuous variable
	arm mechanism	rocker arm mechanism

Air intake valve	OFF	Early closing
Exhaust valve	ON	Normal

When the operation mode of the switching rocker arm mechanism 40 on the exhaust valves 14 and 15 side is set to be on, oil pressure is applied by the oil pressure supply mechanism 80. As shown in FIG. 10, in the switching rocker arm mechanism 40, engine oil is supplied into the hollow portion 71 a. For this reason, the piston 73 rises against the elastic force of the spring 74, and the circumference of the piston 73 is positioned at the window portion 71 b. On the other hand, the roller 41 c moves along the cam 22 by rotation of the cam 22 rotated by the cam shaft 21, and the switching rocker arm 41 oscillates about the rocker shaft 30 at predetermined intervals in a direction indicated by an arrow E in FIG. 8. When the strike arm 41 b is inserted into the window portion 71 b, the strike arm 41 b is brought into contact with the circumference of the piston 73. Therefore, motion of the switching rocker arm 41 is transmitted to the shared rocker arm 60, and the exhaust valves 14 and 15 are driven along a profile of the cam 22. A nose 22 a of the cam 22 corresponds to reference symbol P in FIG. 6.
In the continuous variable rocker arm mechanism 50 on the air intake valves 12 and 13 side, the rocker shaft 30 is rotated counterclockwise by a predetermined angle by means of the drive mechanism 90 and set at an advance angle position. A fulcrum of oscillation of the continuous variable arm 53 is distanced from the air intake valves 12 and 13. In this state, by rotation of the cam 23 rotated by the cam shaft 21, the roller 53 d moves along the cam 23, and the continuous variable arm 53 oscillates about the rocker shaft 30 at predetermined intervals in a direction indicated by an arrow F in FIG. 11. In this manner, motion of the continuous variable arm 53 is transmitted to the shared rocker arm 60 through the transformation member 56 and the intermediate arm 51, and the air intake valves 12 and 13 are driven while being advanced with respect to the profile of the cam 23.
As described above, in an intake stroke of the internal EGR operation, the air intake valves 12 and 13 are driven by the continuous variable rocker arm mechanism 50, and the exhaust valves 14 and 15 are driven by the switching rocker arm mechanism 40. Therefore, the air intake valves 12 and 13 open according to phases and lifts indicated by reference symbol S in FIG. 6, and the exhaust valves 14 and 15 open according to phases and lifts indicated by reference symbol P in FIG. 6. More specifically, the exhaust valves 14 and 15 open at timings indicated by reference symbol P in FIG. 6. That is, since the exhaust valves 14 and 15 open in the intake stroke, an exhaust gas temporarily exhausted from the cylinder 11 is taken into the cylinder 11 to cause an internal EGR operation.
Since the lifts of the exhaust valves 14 and 15 at this time are constant, an amount of internal EGR is constant. On the other hand, since an operation state of the engine is not constant, a required amount of EGR changes. For this reason, this fine adjustment is performed by the operations of the air intake valves 12 and 13. More specifically, in order to prevent a reduction in NO_xfrom being hindered due to an excessively small amount of internal EGR, the end of closing of the air intake valves 12 and 13 is made early to make it possible to reduce an amount of intake itself, and the amount of internal EGR consequently relatively increases. FIG. 7 shows a relationship between closing end phases and amounts of air of the air intake valves 12 and 13 and a relationship between the closing end phases and the amounts of internal EGR of the air intake valves 12 and 13. When the air intake valves 12 and 13 are closed in a phase S1 or S2 slightly earlier than a standard closing end phase S0, an amount of air decreases, and the amount of internal EGR increases.
As described above, the switching rocker arm mechanism 40 and the continuous variable rocker arm mechanism 50 are operated in conjunction with each other to make it possible to obtain a more appropriate amount of EGR and to purify an exhaust gas.
Operations of the switching rocker arm mechanism 40 and the continuous variable rocker arm mechanism 50 in an engine braking operation will be explained while comparing a “normal operation” and an “engine braking operation”. FIG. 12 is a graph showing a relationship between the phase and lift of the cam shaft 21. Reference symbol EX denotes opening valves (lifts) of the exhaust valves 14 and 15, and reference symbol IH denotes opening valves (lifts) of the air intake valves 12 and 13.

The cam shaft 21 causes an exhaust stroke which opens the exhaust valves 14 and 15 to slightly overlap an intake stroke performed by opening the air intake valves 12 and 13. An operation of the switching rocker arm mechanism 40 at this time is shown in FIG. 8, and an operation of the continuous variable rocker arm mechanism 50 at this time is shown in FIG. 9. In the normal operation, on both the air intake valves 12 and 13 side and the exhaust valves 14 and 15 side, an operation mode of the switching rocker arm mechanism 40 is set to be off, and an operation mode of the continuous variable rocker arm mechanism 50 is set to a normal (neutral) mode.
The operation of the switching rocker arm mechanism 40 and the operation of the continuous variable rocker arm mechanism 50 in the normal state will not be explained because the operations are the same as those in FIGS. 8 and 9.

In an engine braking operation, on the air intake valves 12 and 13 side, the operation mode of the switching rocker arm mechanism 40 is set to be off, and the operation mode of the continuous variable rocker arm mechanism 50 is set to a normal (neutral) mode. On the exhaust valves 14 and 15 side, the operation mode of the switching rocker arm mechanism 40 is set to be on, and the operation mode of the continuous variable rocker arm mechanism 50 is set to an early opening (advance) mode.
The operations of the switching rocker arm mechanism 40 and the continuous variable rocker arm mechanism 50 are summarized as follows.

TABLE 2

Engine braking operation

	Switching rocker	Continuous variable
	arm mechanism	rocker arm mechanism

Air intake valve	OFF	Normal
Exhaust valve	ON	Early opening

When the operation mode of the switching rocker arm mechanism 40 on the exhaust valves 14 and 15 side is set to be on, oil pressure is applied by the oil pressure supply mechanism 80. As shown in FIG. 14, in the switching rocker arm mechanism 40, engine oil is supplied into the hollow portion 71 a. For this reason, the piston 73 rises against the elastic force of the spring 74, and the circumference of the piston 73 is positioned at the window portion 71 b. On the other hand, the roller 41 c moves along the cam 22 by rotation of the cam 22 rotated by the cam shaft 21, and the switching rocker arm 41 oscillates about the rocker shaft 30 at predetermined intervals in a direction indicated by an arrow E in FIG. 14. When the strike arm 41 b is inserted into the window portion 71 b, the strike arm 41 b is brought into contact with the circumference of the piston 73. Therefore, motion of the switching rocker arm 41 is transmitted to the shared rocker arm 60, and the exhaust valves 14 and 15 are driven along a profile of the cam 22. The nose 22 a of the cam 22 corresponds to reference symbol L in FIG. 6.
As shown in FIG. 15, in the continuous variable rocker arm mechanism 50 on the exhaust valves 14 and 15 side, the rocker shaft 30 is rotated counterclockwise by a predetermined angle by means of the drive mechanism 90 and set at an advance angle position. A fulcrum of oscillation of the continuous variable arm 53 is distanced from the air intake valves 12 and 13. In this state, by rotation of the cam 23 rotated by the cam shaft 21, the roller 53 d moves along the cam 23, and the continuous variable arm 53 oscillates about the rocker shaft 30 at predetermined intervals in a direction indicated by an arrow F in FIG. 15. In this manner, motion of the continuous variable arm 51 is transmitted to the shared rocker arm 60 through the transformation member 56 and the intermediate arm 51, and the air intake valves 12 and 13 are driven while being advanced with respect to the profile of the cam 23.
As described above, in the engine braking operation, the air intake valves 12 and 13 are driven by the continuous variable rocker arm mechanism 50, and the exhaust valves 14 and 15 are driven by both the switching rocker arm mechanism 40 and the continuous variable rocker arm mechanism 50. Therefore, the air intake valves 12 and 13 open according to phases and lifts indicated by reference symbol N in FIG. 12, and the exhaust valves 14 and 15 open according to phases and lifts indicated by reference symbols M and L in FIG. 12. More specifically, the switching rocker arm mechanism 40 opens the exhaust valves 14 and 15 at timings indicated by reference symbol L in FIG. 12. That is, the exhaust valves 14 and 15 open at a compression top dead center (TDC) to operate a compression brake. Since the lifts of the exhaust valves 14 and 15 are constant, the braking effect is constant.
On the other hand, since the operation state of the engine is not constant, a necessary braking force changes. For this reason, this fine adjustment is performed by the operations of the exhaust valves 14 and 15 driven by the continuous variable rocker arm mechanism 50. More specifically, when the exhaust valves 14 and 15 start to open in a phase M1 or M2 slightly earlier than a standard phase M0 to make an opening timing early, an exhaust energy (amount of air) can be increased, and the braking force is consequently relatively increased. FIG. 13 shows a relationship between opening start phases of the exhaust valves 14 and 15 and the exhaust energy (amount of air) and a relationship between the opening start phases of the exhaust valves 14 and 15 and the engine braking force.
As described above, when the switching rocker arm mechanism 40 and the continuous variable rocker arm mechanism 50 are operated in conjunction with each other, a more appropriate engine braking force can be obtained, and preferable drive feeling can be obtained.
As described above, according to the variable valve apparatus 20 for an internal combustion engine according to the embodiment, a plurality of functions such as execution of internal EGR, application of engine braking, improvement in fuel consumption, and purification of an exhaust gas can be simultaneously exerted.
According to the present invention, valves are opened or closed by using both the switching rocker arm mechanism and the continuous variable rocker arm mechanism to make it possible to realize a plurality of functions such as instantaneous switching of opening/closing timings of the valves and fine control of lifts.
Furthermore, transmission of oscillation displacement is selectively performed as needed to make it possible to open or close a valve without delay. The transmission of oscillation displacement is continuously performed to make it possible to finely control the drive phase and lift of the valve. When fine adjustment of an amount of EGR is performed while performing the internal EGR, an exhaust gas can be purified. Engine braking can be applied, and the effect can be enhanced.

Claims

1. A variable valve apparatus for an internal combustion engine, comprising:

a cam shaft arranged to be rotatable on a cylinder head of the internal combustion engine;

a rocker shaft arranged to be capable of oscillation in the internal combustion engine;

a continuous variable rocker arm mechanism which is driven by a cam formed on the cam shaft, opens or closes at least one of an air intake valve and an exhaust valve, and continuously makes a lift of the valve variable; and

a switching rocker arm mechanism which is driven by the cam formed on the cam shaft, opens or closes at least one of the air intake valve and the exhaust valve, and switches the lift of the valve in a stepwise manner.

2. The variable valve apparatus for an internal combustion engine according to claim 1, wherein

the switching rocker arm mechanism comprises:

a shared rocker arm which is supported on the rocker shaft to be capable of oscillation and configured to drive the valve;

a switching rocker arm which is driven by the cam and arranged to be capable of oscillation on the rocker shaft; and

a transmission mechanism which selectively transmits displacement from the switching rocker arm to the shared rocker arm.

3. The variable valve apparatus for an internal combustion engine according to claim 1, wherein

the continuous variable rocker arm mechanism comprises:

a shared arm supported on the rocker shaft to be capable of oscillation and configured to drive the valve;

a continuous variable arm driven by the cam and arranged to be capable of oscillation about a fulcrum arranged on the rocker shaft side;

an intermediate arm supported by the rocker shaft to be capable of oscillation and arranged between the shared arm and the continuous variable arm;

a transformation member which is arranged between the intermediate arm and the continuous variable arm and transmits oscillation displacement of the continuous variable arm to the shared arm through the intermediate arm; and

a drive mechanism which causes the rocker shaft to oscillate to displace the fulcrum.

4. The variable valve apparatus for an internal combustion engine according to claim 1, wherein

the internal combustion engine comprises the continuous variable rocker arm mechanism on an intake side and the switching rocker arm mechanism on an exhaust side, and

when the internal combustion engine is in an intake stroke, the exhaust valve is opened by the switching rocker arm mechanism, and the air intake valve is closed early by the continuous variable rocker arm mechanism.

5. The variable valve apparatus for an internal combustion engine according to claim 1, wherein

the internal combustion engine comprises at least one of the exhaust valves driven by the switching rocker arm mechanism and at least one of the exhaust valves driven by the continuous variable rocker arm mechanism per cylinder, and

when the internal combustion engine is near a compression top dead center, the exhaust valve is opened by the switching rocker arm mechanism, and the exhaust valve is opened early by the continuous variable rocker arm mechanism.