JPH07217413A - Valve timing control device for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [Purpose] To ensure smooth smooth movement of the spool at all times and improve the valve timing control responsiveness by the phase conversion mechanism. [Structure] A cylindrical gear 5 that converts relative rotation between a sleeve 2 of a camshaft 1 and a timing pulley 4 is moved axially via a servo mechanism 24 of a driving means. The hydraulic chamber 2 is provided on the outer peripheral side of the rear end portion of the sleeve 2.
A communication passage 27e and a drain groove 27d for guiding the working oil discharged from No. 2 to the drain chamber 27c into the rocker cover 16 are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve timing control device for variably controlling the opening / closing timing of an intake valve or an exhaust valve of an internal combustion engine according to the operating condition.

[0002]

2. Description of the Related Art Various conventional valve timing control devices for internal combustion engines have been provided, and one of them is known, for example, as shown in FIG. 1 of Japanese Patent Laid-Open No. 1-134011.

The outline will be described with reference to FIG. 5. A cylindrical sleeve 52 axially connected to one end of a camshaft 50 via a bolt 51, and a ball bearing 53 on the outer circumference of the sleeve 52. And a sleeve 52 which are rotatably arranged relative to each other and are rotationally driven by a crankshaft of the engine via a timing belt.
And a timing pulley 54, and a piston 55 movable in the axial direction. The piston 55 is configured to move forward (to the left in the drawing) by the hydraulic pressure in the hydraulic chamber 56 provided at one end side. Further, between the piston 55 and the timing pulley 54 and the sleeve 52, the sleeve 52, the cam shaft 50 and the timing pulley 54 are moved as the piston 55 moves in the axial direction.
Phase conversion means 57 is provided for converting the relative rotational phase between and.

The hydraulic chamber 56 and the hydraulic supply passage 58 are also provided.
A movable member 60 that interlocks with the piston 55 is slidably provided in the sleeve 52 between the hydraulic pressure release passage 59 and the hydraulic release passage 59, and is slidably fitted in the movable member 60 in the axial direction. A relatively movable spool 61 is provided, and the movable member 60 and the spool 61 form a servo valve. The movable member 60 and the piston 55
Are urged forward by the spring force of the coil spring 57.

Further, the servo valve connects or disconnects the hydraulic chamber 56 and the hydraulic supply passage 58 or the hydraulic release passage 59 by the axial movement of the spool 61. The spool 61 is moved in the axial direction by an electric actuator 62.

When the electromagnetic actuator 62 operates in response to changes in the engine operating state and the hydraulic supply passage 58 and the hydraulic chamber 56 communicate with each other as the spool 61 moves in one direction, the piston 55 causes the spring force of the coil spring 63 to be exerted. Move backwards against. By this, the phase conversion means 57
Converts the relative rotational phase of the cam shaft 50 and the timing pulley 54 to one side.

On the other hand, as the spool 61 moves in the other direction, the hydraulic chamber 56, the hydraulic pressure supply passage 58, and the hydraulic pressure release passage 59 are appropriately communicated with each other, and the piston 55 and the movable member 60 are moved to a predetermined position in front and the cam is moved. The relative rotation phase between the shaft 50 and the timing pulley 54 is continuously converted.

[0008]

However, in the above-mentioned conventional device, the axial hole 5 is formed by penetrating a part of the hydraulic pressure release passage 59 along the internal axial direction of the bolt 51.
Since it is made of 9a, the strength of the bolt 51, particularly the torsional strength, is reduced.

Moreover, the hydraulic pressure release passage 59 has a drain chamber 59b behind the spool valve 61 and an axial hole 59 on the rotation center side.
Since a is used, the hydraulic oil discharge efficiency is reduced. That is, it is discharged from the hydraulic chamber 56 and once the drain chamber 5
The hydraulic oil collected in 9b tries to flow into the axial hole 59a located at the center of rotation, but due to the strong centrifugal force accompanying the rotation of the timing pulley 54, it moves to the outer peripheral side of the drain chamber 59b, and The hydraulic oil cannot be swiftly flowed into the direction hole 59a. Further, the hydraulic pressure in the drain chamber 59b rises, and the hydraulic pressure acts on the spool 61 from the rear surface. Therefore, the electromagnetic actuator 6
If the spool 61 is to be moved to the right in the figure by 2, the reaction force of the hydraulic pressure in the drain chamber 59b will hinder the smooth movement of the spool 61 to the right. As a result, the operating speed of the phase conversion mechanism 57, that is, the relative rotational phase conversion speed of the cam shaft 50 and the timing pulley 54, decreases, and the valve timing control responsiveness may deteriorate.

Further, due to the above-mentioned strong centrifugal force, the hydraulic oil cannot be swiftly flowed into the drain chamber 59b from the hydraulic chamber 56, and in this respect as well, the operational response of the phase conversion mechanism 57 may be deteriorated. There is.

[0011]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned problems of the prior art. The invention of claim 1 is directed to a rotating body which is rotationally driven by an engine, and one end portion thereof from an axial direction. A cam shaft having a cam that operates an intake / exhaust valve by the rotational force transmitted from a rotating body through a fixed sleeve, and a cylindrical body of the rotating body and the sleeve, and are moved in the axial direction. Accordingly, the phase conversion mechanism that converts the relative rotational phase between the rotating body and the camshaft and the hydraulic pressure that is supplied to and discharged from the hydraulic chamber formed inside the tubular body is controlled. A valve timing control device having a driving mechanism having a servo mechanism for controlling the moving position of the hydraulic fluid, the hydraulic fluid being discharged from the hydraulic pressure chamber to the drain chamber inside the sleeve is discharged to the outside on the outer peripheral portion of the sleeve. Provide a drain passage It is characterized in that.

According to a second aspect of the present invention, the downstream end opening of the drain passage is provided inside the rocker cover above the cylinder head.

[0013]

According to the present invention, since the drain passage portion is formed not on the center side of the apparatus but on the outer peripheral portion of the sleeve, the working fluid discharged from the hydraulic chamber to the drain chamber inside the sleeve is centrifugally separated from the rotating body. It can be moved outward by force and can be immediately discharged from the drain passage portion to the outside.

Moreover, since the working fluid flowing into the drain passage is directly discharged into the rocker cover, the working oil is prevented from adhering to the outside of the engine.

[0015]

1 shows an embodiment in which the valve timing control device of the present invention is applied to the intake valve side.

That is, in the figure, reference numeral 1 denotes a cam shaft in which a sleeve 2 is fixed to one end portion 1a of a main body from an axial direction by a mounting bolt 3, and 4 is rotatably provided on the outer circumference of the sleeve 2 of the cam shaft 1, and a cam is provided. Timing pulleys 5 which are rotating bodies for transmitting the rotational force to the shaft 1 are tubular gears which are provided between the sleeve 2 and the timing pulley 4 so as to be movable in the axial direction of the camshaft and which are phase converting means.

The camshaft 1 has a cylinder head 6
Is rotatably supported by a cam bracket 7 provided at the upper end of the, and a cam (not shown) for integrally opening the intake valve against the spring force of the valve spring is provided at a predetermined position on the outer circumference. There is. Further, the sleeve 2 is formed to extend in the axial direction, and one end side is integrally provided with a thin-walled tubular fitting portion 2a that fits into the one end portion 1a of the camshaft main body from the outside. A partition wall 2b is integrally provided on the bottom side of the portion 2a. Further, on the outer circumference of the sleeve 2, outer teeth 2c having a helical tooth shape are formed. Further, the mounting bolt 3 is screwed through the central hole 2d of the partition wall 2b and the bolt hole 1b formed in the axial direction of the camshaft body.

The timing pulley 4 has a cylindrical body 8
A gear portion 9 integrally provided on the outer periphery of the tubular body 8 and having a timing belt wound around the outer periphery thereof; and first and second flanges 10 fixed by caulking to the front and rear ends of the tubular body 8. 1
1 and a helical tooth-shaped inner tooth 8a is formed on the inner circumference of the rear end side of the cylindrical main body 8.

In the first and second flanges 10 and 11, the inner peripheral surfaces of the fixed base portions 10a and 11a are slidably supported on the outer peripheral surface of the sleeve 2, and the entire timing pulley 4 is located on the outer peripheral surface of the sleeve 2. On the other hand, it is supported at two front and rear points around the gear portion 9. A disk-shaped front cover 12 is liquid-tightly fixed to a front end portion of the first flange portion 10 via a C ring 13 and a seal ring 14, and an interlocking portion described later is provided on an inner peripheral side of the fixed base portion 10a. A plurality of shaft insertion holes 10b through which the shaft 36 is inserted are formed at equidistant positions in the circumferential direction. In addition, this one shaft insertion hole 10
A drain hole 15 is axially formed on the outer peripheral side of b. A seal member 17 that seals the inside of the rocker cover 16 is provided between the cylindrical portion 11b provided on the inner peripheral side of the second flange 11 and the flange portion of the rocker cover 16. .

The tubular gear 5 has an annular groove 18 on the inner and outer circumferences.
A and 18b are formed, and inner and outer teeth 5a and 5b in the form of a helical tooth that mesh with the inner teeth 8a and the outer teeth 2c are formed on the inner and outer circumferences of the rear end portion. Also, the front end is
The inner and outer peripheral surfaces are slidably guided to the inner surface of the cylindrical main body 8 and the outer surface of the sleeve 2, and the hydraulic chamber 2 to be described later is inserted in the annular groove of the inner and outer peripheral surfaces.
Seal rings 19 and 20 for sealing 2 are fitted and fixed. Further, the tubular gear 5 is adapted to move in the axial direction by the driving means.

The driving means is elastically mounted between the inner end surface of the first flange 10 and the inner bottom surface of the tubular gear 5 to urge the tubular gear 5 in the rearward direction, and the tubular shape. A hydraulic chamber 22 formed between the annular grooves 18a and 18b on the inner and outer circumferences of the gear 5 and the tubular main body 8 and the sleeve 2, a hydraulic circuit 23 for supplying and discharging hydraulic pressure to and from the hydraulic chamber 22, and the inside of the hydraulic chamber 22. And a servo mechanism 24 for controlling the moving position of the cylindrical gear 5 by controlling the discharge amount of the hydraulic oil.

The hydraulic circuit 23 discharges the hydraulic oil in the hydraulic chamber 22 into the rocker cover 16 and the supply passage 26 whose upstream end is connected to the main gallery 25 for supplying lubricating oil to each sliding portion of the engine. And a discharge passage 27 for discharging.

The supply passage 26 has a main gallery 25.
The lubricating oil in the oil pan is introduced through the strainer by the oil pump 28 provided on the upstream side of the above, and the downstream end is connected to the hydraulic chamber 22. That is, the supply passage 26 includes an oil passage portion 26a formed inside the cylinder head 6 and along the radial direction of the cam shaft 1, the central hole 2d, and the bolt insertion hole 1b.
Between the mounting bolt 3 and the outer peripheral surface of the mounting bolt 3, the oil passage 26
It has an annular passage portion 26b communicating with a, and a supply hole 26c which is formed in a substantially L shape on the lower end side in the drawing of the rear end portion of the peripheral wall of the sleeve 2 and has one end facing the annular passage portion 26b. The supply hole 26c has a movable cylindrical body 32 whose other end in the inclined shape will be described later.
Through a first guide groove 26d formed on the outer periphery of the outer peripheral surface of the peripheral wall of the peripheral wall. Also, this first
The radial hole 26e communicates with a second radial hole 29 formed on the opposite side of the first radial hole 26e via an annular groove 26f provided on the outer periphery of the spool valve 33 on the rear end side, and further the sleeve 2 Inclined passage portion 30 formed in an inclined shape on the peripheral wall of the
Through the hydraulic chamber 22. A second guide groove 29a is formed at the outer end of the second radial hole 29.

On the other hand, the discharge passage 27 is formed by the inclined passage portion 3
0, the second guide groove 29a and the second radial hole 29,
It is formed along the radial direction on the front end side of the spool valve 33,
A through hole 27b that communicates with the second radial hole 29 via a groove groove 27a on the outer circumference, and a drain chamber 27 that is separated inside the spool valve 33, the sleeve 2, etc. and communicates with the through hole 27b.
c and a drain groove 27d which is formed in an inclined shape on the upper end side of the rear end portion of the sleeve 2 and is formed along the axial direction on the inner periphery of the tubular portion 11b so that the outer end opening faces the rocker cover 16.
And a communication passage 27e that communicates the inside of the rocker cover 16 and the drain chamber 27c through the drain groove 27d, and the communication passage 27e and the drain groove 27d form a drain passage portion. Further, the first flange 1 is provided on the outer periphery of the front end of the spool valve 33 via the groove groove 27a.
The hydraulic oil collected in the working chamber 31 inside
An oil groove 27f for returning to the inside of c is formed.

The servo mechanism 24 is provided on the inner periphery of the sleeve 2 so as to be slidable in the axial direction, and on the inner periphery of the movable barrel 32 so as to be slidable in the axial direction. A spool valve 33, an electromagnetic actuator 34 that is fixed to the belt cover 57 and presses the spool valve 33 to the right in the figure, and a controller 35 that controls the operation amount of the electromagnetic actuator 34 according to the engine operating state. I have it.

The movable cylindrical body 32 is integrally provided with a flange portion 32a at a front end portion protruding from the tip end of the sleeve 2, and an outer peripheral portion of the flange portion 32a is formed larger than the outer diameter of the sleeve 2. . Further, the shaft insertion hole 10b is slidably inserted between the inner end surface of the outer peripheral portion of the flange portion 32a and the front end portion of the tubular gear 5 so that the tubular gear 5 moves forward as the tubular gear 5 moves. A plurality of interlocking shafts 36 that synchronously move the movable tubular body 32 are interposed. In addition, this movable cylinder 32
Is urged to the rearward moving position by the spring force of the coil spring 37 elastically mounted between the inner peripheral portion and the front cover 12, and the flange portion 32 a is always connected to the front end portion of the tubular gear 5 via the interlocking shaft 36. It comes into contact with. Further, the free end of the interlocking shaft 36 is fitted into the restriction groove 32b formed on the inner end surface of the collar portion 32a to restrict the free rotation of the movable cylindrical body 32.

The spool valve 33 has a cylindrical shape with a bottom,
The spring force of a coil spring 38 elastically mounted between the inner surface of the bottom wall and the head of the mounting bolt 3 urges it to the front position (in the left direction in the drawing), and the outer surface of the bottom wall has a sliding shaft. One end of 39 is in contact with from the axial direction. The sliding shaft 39 slidably penetrates through the center hole of the front cover 12 via a seal ring 40, and has the other end at the electromagnetic actuator 3
The drive shaft 41 of No. 4 is in contact from the axial direction.

The electromagnetic actuator 34 includes an electromagnetic coil 43 in a cylindrical body 42, a fixed core 44 that is excited by energization of the electromagnetic coil 43, and the fixed core 4.
The movable core 45 and the like to be sucked by 4 are stored. The movable core 45 has a drive rod 41 fixed to the front end thereof and is urged rightward in the figure by a spring member 46 elastically mounted on the rear end side, so that the front end edge of the drive rod 41 slides along the slide shaft 39. Is always in contact with the other end of the.

The controller 35 detects a current engine operating state based on an information signal output from a built-in microcomputer such as a crank angle sensor, an air flow meter, a water temperature sensor, and a throttle valve switch. Then, a control current is output to the electromagnetic coil 43 of the actuator 34 according to the operating state.

The operation of this embodiment will be described below.

First, in the engine low load range, the controller 3
5, the maximum control current is output to the electromagnetic actuator 34, the drive rod 41 advances as shown in FIG. 1, and the sliding shaft 39 is pushed into the working chamber 31. Therefore, the spool valve 33 moves to the maximum right end position as shown in the figure against the spring force of the coil spring 38, and immediately after the movement, the second radial hole 30 and the groove groove 29a temporarily communicate with each other. For this reason, the hydraulic oil in the hydraulic chamber 22 is discharged through the through hole 29 and the drain chamber 27.
c, it is collected from the drain passage 27d through the communication passage 27e. Therefore, as the pressure in the hydraulic chamber 22 is reduced, the tubular gear 5 moves to the maximum rearward position as shown by the spring force of the compression spring 21. Therefore, the movable cylindrical body 32 also follows and moves in the same direction as the cylindrical gear 5 with the same stroke amount via the interlocking shaft 36, so that the second radial hole 29 is formed on the outer peripheral surface of the spool valve 33 as shown in the drawing. It is blocked and communication is cut off.

Accordingly, the camshaft 1 and the timing pulley 4 are converted into a relative rotational phase determined by the maximum rearward position of the tubular gear 5, and retard the closing timing of the intake valve.

Next, when a predetermined medium load region is entered, a predetermined control current is simultaneously output to the electromagnetic actuator 34, and the drive shaft 41 moves slightly to the left as shown in the figure, so that the spool valve 33 also coil. The spring force of the spring 38 causes the spring 38 to move slightly to the left, and the annular groove 26f and the second radial hole 2
9 communicate. Therefore, the hydraulic oil pressure-fed from the oil pump 28 is transferred to the oil passage portion 26a, the annular passage portion 26b,
Supply hole 26c, first guide groove 26d, first radial hole 2
6e, annular groove 26f, second radial hole 29, inclined passage 3
It is supplied to the hydraulic chamber 22 through 0.

As a result, the cylindrical gear 5 moves forward from the position shown in FIG. 2 against the spring force of the compression spring 21, and at the same time, the movable cylindrical body 32 also moves in the same direction with the same stroke amount. Therefore, the communication between the second radial hole 29 and the annular groove 26f is blocked. In other words, both 29 and 26f
The movable cylinder 32 moves until the spool valve 3 is closed.
The cylindrical gear 5 moves forward (leftward) by the amount of the movement of 3 to the left, and is stably held at the position where the communication between the two 29, 26f is blocked. Therefore, the camshaft 1 and the timing pulley 4 relatively rotate to one side in accordance with the moving position of the tubular gear 5 to control the closing timing of the intake valve to the slightly advanced side.

On the other hand, when the engine is under high load, the electromagnetic actuator 34 is de-energized, and therefore the spool valve 33
Moves to the maximum leftward position by the spring force of the coil spring 38 as shown in FIG. 3, and at the time of this movement, the annular groove 26f and the second radial hole 29 communicate with each other with the maximum opening area. For this reason,
The hydraulic oil is sufficiently supplied from the supply passage 26 into the hydraulic chamber 22, and the internal pressure of the hydraulic chamber 22 rises.

Therefore, when the tubular gear 5 moves to the maximum forward position as shown, the movable tubular body 32 also moves in the same direction at the same time, and eventually the second radial hole 29 and the annular groove 26f.
Communication with is cut off. Thereby, the cylindrical gear 5 is
The camshaft 1 and the timing pulley 4 are relatively rotated to the one side at the maximum while being held at the maximum front position, and the intake valve closing timing is controlled to the maximum advance angle.

When the high load region is shifted to the predetermined medium load region, the spool valve 33 is moved slightly to the right as shown in FIG. 4, and the second radial hole 29 and the groove groove are moved during this movement. 27a is communicated. Therefore, a part of the hydraulic oil in the hydraulic chamber 22 is collected in the rocker cover 16 from the discharge passage 27. Therefore, the tubular gear 5 moves slightly backward from the position shown in FIG. 4, and at the same time, the movable tubular body 32 also moves in the same direction, and eventually the second radial hole 29 and the groove groove 2 are formed.
The communication of 7a is cut off. Thereby, the tubular gear 5
Is held at a predetermined intermediate position and controls the closing timing of the intake valve to a slightly retarded side based on the relative rotational phase of the camshaft 1 and the timing pulley 4 determined at such position.

Therefore, according to this embodiment, since the moving position of the cylindrical gear 5 can be controlled steplessly according to the engine operating state, the valve timing can be controlled with high accuracy. As a result, engine performance, that is, performance such as improvement of combustion efficiency at low load and output improvement at high load, can be greatly improved.

Further, as described above, the hydraulic oil discharged from the hydraulic chamber 22 to the drain chamber 27c through the inclined passage portion 30, the second radial hole 29, the groove groove 27a, and the through hole 27b is supplied to the timing pulley 4 or the timing pulley 4. The sleeve 2 is moved to the outer peripheral side of the drain chamber 27c by the rotational centrifugal force of the sleeve 2, and immediately flows into the communication passage 27e and the drain groove 27d as it is, and is recovered inside the rocker cover 16. Therefore, the efficiency of discharging the hydraulic oil is improved, and the increase of the hydraulic pressure in the drain chamber 27c can be sufficiently suppressed. Therefore, the influence of the hydraulic pressure in the drain chamber 27c on the spool valve 33 is surely avoided, and the sliding action of the spool valve 33 is always smooth.

Moreover, since the working oil is discharged directly into the rocker cover 16 rather than outside the engine, the timing pulley 4 is prevented from adhering to the gear portion 9. As a result, not only the deterioration of the timing belt,
The occurrence of slip with the gear unit 9 can be prevented.

The hydraulic oil flowing from the communication passage 27e into the drain groove 27d is used for the inner peripheral surface of the cylindrical portion 11b and the sleeve 2.
Since lubrication is provided between the outer peripheral surface and the outer peripheral surface, the relative sliding action of both 11b and 2 is smooth.

Further, since the timing pulley 4 is supported by the flanges 10 and 11 at the two points at the front and rear ends of the sleeve 2, the timing pulley 4 is not tilted by the tension load of the timing belt and is always in the axial center of the camshaft 1. A horizontal posture is maintained. Therefore, the occurrence of an eccentric load on the cylindrical gear 5 is prevented, and smooth movability in the axial direction is always obtained. As a result, the relative rotational phase conversion speed of the camshaft 1 and the timing pulley 4 is increased, and the valve timing control response is also improved.

When the apparatus is assembled, the cylindrical main body 8
And the first and second flanges 10 and 11, the tubular gear 5, the compression spring 21, and the sleeve 2 are assembled in advance to form a unit, and this unit is attached to the camshaft 1 with a mounting bolt 3
Since the interlocking shaft 36, the movable cylinder 32, the spool valve 33, the front cover 12 and the like can be sequentially assembled by tightening and fixing, the assembly workability is improved.

[0044]

As is apparent from the above description, according to the present invention, the working fluid discharged into the drain chamber in the sleeve is
The centrifugal force of rotation of the rotor and the sleeve causes the sleeve to move toward the inner peripheral side of the sleeve and quickly flow into the drain passage. Therefore, the influence of the hydraulic pressure in the drain chamber on the spool valve is avoided, and smooth movement of the spool valve is always ensured. As a result, the movement responsiveness of the phase conversion mechanism is improved, and the valve timing control responsiveness to changes in the engine operating state is improved.

Moreover, the hydraulic fluid that has flowed into the drain passage is collected inside the rocker cover, not outside the engine, so that it is prevented from adhering to the rotating body or the like. For example, deterioration of the timing belt or the timing belt. It is possible to prevent the occurrence of slip between the rotor and the rotating body.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the operation of the present embodiment.

FIG. 3 is an explanatory diagram showing the operation of the present embodiment.

FIG. 4 is an explanatory diagram showing the operation of the present embodiment.

FIG. 5 is a vertical sectional view showing a conventional valve timing control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Camshaft 2 ... Sleeve 4 ... Timing pulley (rotating body) 5 ... Cylindrical gear (phase conversion means) 22 ... Hydraulic chamber (hydraulic chamber) 24 ... Servo mechanism 26 ... Supply passage 27 ... Discharge passage 27d ... Drain groove (Drain passage part) 27e ... Communication passage (drain passage part) 27c ... Drain chamber

Claims (2)

[Claims] 1. A rotating body which is rotationally driven by an engine, a cam shaft having a cam which operates an intake / exhaust valve by a rotational force transmitted from the rotating body through a sleeve axially fixed to one end, and a rotating body. A phase conversion mechanism, which is interposed between the tubular main body of the body and the sleeve, converts the relative rotational phase of the rotary body and the cam shaft with axial movement, and is formed inside the tubular main body. A valve timing control device comprising: a drive unit having a servo mechanism for controlling the hydraulic pressure supplied to and discharged from the hydraulic chamber, and controlling the moving position of the phase conversion mechanism. A valve timing control device for an internal combustion engine, comprising: a drain passage portion that discharges the hydraulic fluid discharged from the hydraulic chamber to the drain chamber in the sleeve to the outside. 2. The valve timing control device for an internal combustion engine according to claim 1, wherein a downstream end opening of the drain passage is provided inside the rocker cover above the cylinder head.