JP4858119B2 - Cylinder head structure - Google Patents

Description

  The present invention relates to a cylinder head structure including a camshaft bracket of a ladder frame structure that supports an intake / exhaust cam mechanism together with a cylinder head of an internal combustion engine.

  Conventionally, in order to improve the support rigidity of the camshaft bearing, it is made of a metal material having the same rigidity and strength as the cylinder head, such as aluminum alloy or cast iron, and both ends of each upper side bearing cap of the camshaft journal. Has been proposed that includes a camshaft bracket having a ladder frame structure that is integrated in a ladder shape over an outer frame portion provided along the opening edge of the cylinder head (see Patent Document 1).

Then, the edge portion of the upper opening of the camshaft bracket of the ladder frame structure is formed flat, and a flat annular gasket is sandwiched between the upper openings, and the die is integrally molded with a lightweight and inexpensive synthetic resin material. The space for covering the cam mechanism is covered with a rocker cover so as to be sealed. The front end frame of the camshaft bracket (front end side of the outer frame) is raised upward and integrated with the front end of the cylinder head and cylinder block, and the front for accommodating the cam drive chains equipped in front of them. The cover mounting surface is configured.
JP 2005-113850 A

  By the way, when the variable valve mechanism is applied to the conventional cylinder head structure, it is necessary to process the control shaft journal on the camshaft bracket in order to arrange the control shaft in addition to the drive shaft corresponding to the camshaft. There is. Here, in order to machine the control axis journal with high accuracy, it is necessary to introduce the tool in the longitudinal direction of the camshaft bracket (crankshaft direction). However, since the camshaft bracket is a ladder frame shape, the tool is a camshaft bracket. Interferes with the front and rear frame.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a cylinder head structure including a camshaft bracket having a ladder frame structure to which a variable valve apparatus can be applied.

According to the present invention, a frame portion that is overlapped with a frame portion that is formed on the outer peripheral portion of the upper surface of the cylinder head and a plurality of bracket portions that connect the opposing frame portions in a ladder shape are integrally formed, and the plurality of bracket portions and brackets A camshaft bracket that forms a journal support portion for the drive shaft of the exhaust camshaft and intake variable valve mechanism between the front and rear frame portions facing each other in parallel with the cylinder head, and a front surface of the camshaft bracket and the cylinder head And a front cover that houses a cam sprocket and a timing chain or timing belt, and a plurality of holes are machined on the same axis in a frame portion to which the front cover of the camshaft bracket is joined. The outer circumference of the tool so that it holds the tool It has been over forming comprises forming a hole through which the said tool.

  Therefore, in the present invention, the hole formed in the frame part to which the front cover of the camshaft bracket is joined can be used as a hole through which a tool for machining the journal support part of the control shaft in the intake variable valve mechanism is passed. .

  For this reason, the hole that penetrates the tool formed in the frame part of the camshaft bracket supports the control axis journal by holding and guiding the machining tool when machining the journal support part of the control axis of the intake variable valve mechanism. The processing accuracy of the part can be improved.

  Hereinafter, an embodiment of a cylinder head structure of the present invention will be described with reference to FIGS. 1 is a side view of a cylinder head structure according to an embodiment of the present invention, FIG. 2 is a plan view of the cylinder head structure, FIG. 3 is a front view of the cylinder head structure, and FIG. 5 is a perspective view of a camshaft bracket and a cylinder head in a cylinder head structure, FIG. 6 is an enlarged perspective view of the main part in FIG. 5, FIG. 7 is a configuration diagram of an intake variable valve mechanism, and FIG. 8 is a second embodiment. It is a front view of the cylinder head structure.

  The internal combustion engine in the present embodiment is a V-type 6-cylinder engine, the intake side is disposed inside the opposite V-type bank, the exhaust side is disposed outside the V-type bank, and placed horizontally or vertically in the engine room. It is an engine of a vehicle that is installed in a place. Here, the side on which the transmission for shifting the output of the engine is mounted is referred to as the rear, the opposite side is referred to as the front, and for each bank, the tip side of each V-type is referred to as the upper side, and the opposite side is referred to as the lower side. To do. Further, only the right bank disposed on the right side toward the front will be described, but the left bank is similarly configured.

  As shown in FIGS. 1 to 4, the cylinder head structure of the present embodiment includes a cylinder head 1, a camshaft bracket 2 having a ladder frame structure that is stacked on the cylinder head 1, and an upper opening of the camshaft bracket 2. A rocker cover 3 for covering, a camshaft bracket 2 and a front cover 4 fixedly disposed on the front surface of the cylinder head 1 are provided. Between the cylinder head 1 and the camshaft bracket 2, an exhaust camshaft 5 having an exhaust cam for driving the exhaust valve to open and close and an intake variable valve mechanism 6 for opening and closing the intake valve are supported.

  First, the intake variable valve mechanism 6 will be described. The intake variable valve mechanism 6 is a variable valve mechanism that makes the intake valve opening / closing timing variable, and will be described with reference to FIG. The intake valve side variable valve mechanism of the internal combustion engine includes a lift / operation angle variable mechanism 51 that changes the lift / operation angle of the intake valve, and a phase (phase with respect to a crankshaft (not shown)) of the lift is advanced or The phase variable mechanism 71 for retarding the angle is combined.

  The lift / operating angle variable mechanism 51 will be described first. The lift / operating angle variable mechanism 51 has been previously proposed by the applicant of the present application. However, since it has been publicly known, for example, in Japanese Patent Application Laid-Open No. 11-107725, only the outline thereof will be described. The lift / operating angle variable mechanism 51 includes a drive shaft 52 rotatably supported by a cam bracket (not shown) above the cylinder head, an eccentric cam 53 fixed to the drive shaft 52 by press-fitting, and the like. A control shaft 62 that is rotatably supported by the same cam bracket at a position above the drive shaft 52 and arranged in parallel to the drive shaft 52, and a rocker arm that is swingably supported by an eccentric cam portion 68 of the control shaft 62. 56 and a swing cam 59 that abuts against the tappet 60 disposed at the upper end of each intake valve 61.

  The eccentric cam 53 and the rocker arm 56 are linked by a link arm 54, and the rocker arm 56 and the swing cam 59 are linked by a link member 58. The drive shaft 52 is driven by the crankshaft of the engine via a timing chain or a timing belt. The eccentric cam 53 has a circular outer peripheral surface centered at a point offset from the shaft center of the drive shaft 52 by a predetermined amount, and an annular portion of the link arm 54 is rotatably fitted to the outer peripheral surface. Yes.

  The rocker arm 56 has a substantially central portion supported by the eccentric cam portion 68 so as to be swingable. The one end portion of the rocker arm 56 is linked to the arm portion of the link arm 54 via a connecting pin 55 and the other end portion. Further, the upper end portion of the link member 58 is linked via the connecting pin 57. The eccentric cam portion 68 is eccentric from the axis of the control shaft 62, and the rocking center of the rocker arm 56 changes according to the angular position of the control shaft 62.

  The swing cam 59 is fitted to the outer periphery of the drive shaft 52 and is rotatably supported, and a lower end portion of the link member 58 is linked to an end portion extending sideways through a connecting pin 67. . On the lower surface of the swing cam 59, a base circle surface concentric with the drive shaft 52 and a cam surface extending in a predetermined curve from the base circle surface are continuously formed. The base circle surface and the cam surface come into contact with the upper surface of the tappet 60 according to the swing position of the swing cam 59. In other words, the base circle surface is a section where the lift amount becomes 0 as a base circle section, and when the swing cam 59 swings and the cam surface contacts the tappet 60, the base circle section lifts gradually. A slight lap section is provided between the base circle section and the lift section.

  The control shaft 62 is configured to rotate within a predetermined angle range by a lift / operating angle control actuator 63 provided at one end. The lift / operating angle control actuator 63 includes, for example, a servo motor that drives the control shaft 62 via the worm gear 65, and is controlled by a control signal from the engine control unit 69. The rotation angle of the control shaft 62 is detected by the control shaft sensor 64.

  When the drive shaft 52 rotates, the lift / operating angle variable mechanism 51 configured as described above moves the link arm 4 up and down by the cam action of the eccentric cam 53, and the rocker arm 56 swings accordingly. The swing of the rocker arm 56 is transmitted to the swing cam 59 via the link member 58 to swing the swing cam 59. By the cam action of the swing cam 59, the tappet 60 is pressed and acts to lift the intake valve 61.

  When the angle of the control shaft 62 is changed via the lift / operation angle control actuator 63, the initial position of the rocker arm 56 changes and the initial swing position of the swing cam 59 changes. For example, if the eccentric cam portion 68 is positioned upward in the figure, the rocker arm 56 is positioned upward as a whole, and the end of the swing cam 59 on the side of the connecting pin 67 is relatively lifted upward. Become. That is, the initial position of the swing cam 59 is inclined in a direction in which the cam surface is separated from the tappet 60. Therefore, when the swing cam 59 swings with the rotation of the drive shaft 52, the base circle surface is kept in contact with the tappet 60 for a long time, and the period during which the cam surface is in contact with the tappet 60 is short. Therefore, the lift amount is reduced as a whole, and the angle range from the opening timing to the closing timing, that is, the operating angle is also reduced.

  On the contrary, if the eccentric cam portion 68 is positioned downward in the figure, the rocker arm 56 is positioned downward as a whole, and the end portion on the connecting pin 67 side of the swing cam 59 is pushed downward relatively. It becomes a state. That is, the initial position of the swing cam 59 is inclined in a direction in which the cam surface approaches the tappet 60. Therefore, when the swing cam 59 swings with the rotation of the drive shaft 52, the portion that contacts the tappet 60 immediately shifts from the base circle surface to the cam surface. Therefore, the lift amount is increased as a whole, and the operating angle is increased.

  Since the initial position of the eccentric cam portion 68 can be continuously changed, the valve lift characteristic is continuously changed accordingly. That is, the lift and the operating angle can be continuously expanded and reduced simultaneously. Depending on the layout of each part, for example, the opening timing and closing timing of the intake valve 61 change substantially symmetrically with the change in the lift and operating angle.

  The phase variable mechanism 71 includes a sprocket 72 provided at a front end portion of the drive shaft 52, and a phase control actuator 73 that relatively rotates the sprocket 72 and the drive shaft 52 within a predetermined angle range. , Is composed of. The sprocket 72 is linked to the crankshaft via a timing chain or timing belt (not shown). The phase control actuator 73 is composed of, for example, a hydraulic or electromagnetic rotary actuator, and is controlled by a control signal from the engine control unit 69. Due to the action of the phase control actuator 73, the sprocket 72 and the drive shaft 52 rotate relatively, and the lift center angle in the valve lift is retarded.

  In other words, the lift characteristic curve itself does not change, and the whole advances or retards. This change can also be obtained continuously. The control state of the phase variable mechanism 71 is detected by a drive shaft sensor 66 that responds to the rotational position of the drive shaft 52. The control of the lift / operating angle variable mechanism 51 and the phase variable mechanism 71 is optimally controlled by the ECU together with the engine operating conditions. The cycle variable stroke engine of this embodiment provided with the variable valve mechanism described above on the intake valve side can also control the intake air amount by variable control of the intake valve 61 without depending on the throttle valve.

  1 to 4, the cylinder head 1 is made of an aluminum alloy, and includes three combustion chambers formed with cylinder bores of a cylinder block (not shown) below. The cylinder head 1 is connected to each combustion chamber and has one side wall. An intake port P is formed from the side surface (front side in FIG. 1), and an exhaust port is formed from the other side wall. Although not shown, an intake valve is disposed at a portion connected to the intake port of the combustion chamber, and an exhaust valve is disposed at a portion connected to the exhaust port. A lower half portion of the annular mounting surface 10 of the front cover 4 that accommodates the timing chains 34 and 36 and the cam sprockets 31, 33, and 73 is formed on the front surface of the cylinder head 1.

  As shown in FIGS. 5 and 6, the upper surface of the cylinder head 1 is raised at the outer peripheral portion thereof, and forms a seal line with a peripheral frame portion 21 of the camshaft bracket 2 described later. The rib 12 and the front and rear frame portions 11 that are formed in a state where the left and right frame portions 11 are connected to each cylinder and the front and rear frame portions 11 are journals of the drive shaft 52 of the intake variable valve mechanism 6 that opens and closes the intake valve. And a journal support portion 13 for supporting the journal of the exhaust side camshaft 5 from below. At the center of each rib 12, there is formed a threaded portion for attaching a spark plug to the combustion chamber.

  As shown in FIGS. 2 and 5, the camshaft bracket 2 is overlapped with the peripheral frame portion 21 that overlaps the frame portion 11 of the cylinder head 1 and the rib 12 of the cylinder head 1, and the left and right frame portions 21. Bracket portions 22 of camshafts (exhaust camshaft 5 and drive shaft 52 of intake variable valve mechanism 6), and the intake variable valve mechanism branched from the center of each bracket portion 22 to the front. A ladder frame structure having a control shaft bracket portion 22A connected to the left frame portion 21 across the six drive shafts 52 is integrally cast with an aluminum alloy. The bracket portion 22 and the front and rear frame portions 21 of each camshaft support the journal of the drive shaft 52 of the intake variable valve mechanism 6 that opens and closes the intake valve and the journal of the exhaust side camshaft 5 from above. A journal support portion 23 is provided. Further, a plug hole 22B for accommodating a spark plug is formed in the center of the bracket portion 22 of each camshaft.

  A journal support portion 23A for supporting the journal of the control shaft 62 from below is formed on the upper surface of each control shaft bracket 22A, and a bearing provided with a journal support portion 23B for supporting the journal from above on the upper portion thereof. The cap 24 is fixed.

  The camshaft bracket 2 is provided with mounting holes (in the brackets 22 and 22A) with the journals of the exhaust camshaft 5 and the journals of the drive shaft 52 of the intake cam mechanism 6 interposed between the camshaft bracket 2 and the cylinder head 1. Nine locations in the illustrated example), mounting holes (three locations in the illustrated example) provided at the joint between the control shaft bracket 22A and the camshaft bracket 22 in the left frame portion 21, and the front frame portion 21. The fixing bolts 25 are respectively inserted into the mounting holes (four in the illustrated example), and the bolts 25 are screwed into the screw holes provided in the cylinder head 1, thereby being fixed integrally to the cylinder head 1. The rear frame portion 21 is similarly fixed by bolts.

  As shown in FIGS. 4 to 6, the front frame portion 21 is raised upward, and on the front surface thereof is a ring to the front cover 4 that houses the timing chains 34 and 36 and the cam sprockets 31, 33, and 73. An upper half portion of the mounting surface 10 is formed. Further, on the back surface of the front frame portion 21, an arch surface 26 that is continuous with the upper surfaces of the left and right frame portions 21 and is raised in an arch shape on the back surface of the front frame portion 21 is formed. A housing 27 that houses an actuator that controls the rotational position of the control shaft 62, for example, a worm gear mechanism and a servo motor, is fixed above the rear frame portion 21. An arch surface 27 </ b> A that is continuous with the upper surface of the frame portion 21 and is raised in an arch shape on the front surface of the housing 27 is formed.

  The front frame portion 21 and the arch surfaces 26 and 27 </ b> A of the rear housing 27 and the upper surfaces of the left and right frame portions 21 constitute a seal line with the rocker cover 3. The rocker cover 3 is integrally formed of a lightweight and inexpensive synthetic resin material, and is formed by upper surfaces of the left and right frame portions 21 of the camshaft bracket 2, an arch surface 26 of the front frame portion 21, and an arch surface 27 A of the rear housing 27. An annular mounting surface 3A that joins the formed seal line is provided. The rocker cover 3 is attached to the camshaft bracket 2 with a bolt (not shown) by laminating the annular mounting surface 3A via a gasket between the rocker cover 3 and the seal line.

  As shown in FIGS. 3 and 4, the front end of the exhaust camshaft 5 and the drive shaft 52 of the intake variable valve mechanism 6 are arranged to protrude from the front surface of the front frame portion 21. The exhaust cam sprocket 31 is fixed, and the intake cam sprockets 72 and 33 are fixed to the outer periphery of a drum case 32 incorporating a phase variable mechanism at the tip of the drive shaft 52 on the intake side. A secondary timing chain 34 is arranged around the belt 33. The secondary timing chain 34 is tensioned by a secondary chain tensioner 35 and is prevented from loosening. A part of the casing of the tensioner 35 is accommodated in a space recessed in the front surface of the front end frame portion 21 of the camshaft bracket 2.

  A cam sprocket 72 is fixed to the outer periphery of the drum case 32 having a built-in phase variable mechanism, and a primary timing chain 36 wound around a crank sprocket arranged at the front end of a crankshaft (not shown) is wound around the cam sprocket 72. It is hung.

  The front cover 4 has a joint surface 10 (surface perpendicular to the camshaft axis) provided on the front surface of the cylinder head 1 and the camshaft bracket 2 coupled to the joint surface 10 via a gasket. The supply / exhaust cam sprockets 31 and 33, the secondary timing chain 34, the cam sprocket 72, the primary timing chain 36, and the drum case 32 disposed in front of the cylinder head 1 and the camshaft bracket 2 are accommodated therebetween. To do.

  The exhaust camshaft 5 formed by the cylinder head 1 and the camshaft bracket 2 and the journal support portions of the drive shaft 52 of the intake variable valve mechanism 6, the control shaft 62 formed by the camshaft bracket 2 and the bearing cap 24. Each journal support portion is formed by punching the assembled assembly.

  That is, as shown in FIGS. 5 and 6, the camshaft bracket 2 is fixed by interposing a gasket in the cylinder head 1, and the bearing cap 24 is fixed to the camshaft bracket 2 to form an assembly. The assembly is fixed to a machine tool, and the front end frame portion 11 of the cylinder head 1 and the front end of the camshaft bracket 2 are drilled on the same axis with a processing tool such as a drill from the front side of the assembly. Both the frame portion 21 and the ribs 12 of the cylinder head 1 and the brackets 22 of the camshaft bracket 2 are each drilled so as to have the same axis line. Each journal support portion of the drive shaft 52 of the variable valve mechanism 6 is formed.

  Further, each journal support portion of the control shaft 62 is formed by drilling holes in the front end frame portion 21 of the camshaft bracket 2 and the camshaft bracket 2 and the bearing cap 24 so as to have the same axis. . The hole 37 formed in the front end frame portion 21 of the camshaft bracket 2 is not used as a journal support portion of the control shaft 62, but functions as a guide that guides and holds the tool while preventing the tool from shaking during drilling. The processing accuracy of the journal support portion of the control shaft 62 can be improved. Further, the hole 37 communicates the space formed by the cylinder head 1 / cam shaft bracket 2 and the rocker cover 3 with the timing chain housing space formed by the front cover 4 / cam shaft bracket 2 and the cylinder head 1. A road is also constructed.

  According to the cylinder head structure having the above configuration, in addition to the processing of the journal support portion of the exhaust camshaft 5 and the drive shaft 52 of the intake variable valve mechanism 6 on the front end frame portion 21 of the camshaft bracket 2 having a ladder frame structure. An arch-shaped seal line 26 joined to the mounting surface 3A of the rocker cover 3 over the tool through hole formed at the time of processing the journal support portion of the control shaft 62 of the intake variable valve mechanism 6 to be implemented. Are integrally formed. Since it is the said arch-shaped seal line 26, the said tool through-hole 37 can be included below, without raising the seal line 26 entirely, and the camshaft bracket 2 can be reduced in size. Further, both the arch-shaped seal line 26 and the seal lines on both sides extending in the front-rear direction connected to both ends of the arch-shaped seal line 26 can be formed on the camshaft bracket 2, and a front cover that is a separate part from the upper end surface of the cylinder head as in the conventional example. The problem caused by the level difference that occurs when the seal line is formed with the upper end surface is eliminated, and the sealing performance can be improved. In addition, since the front cover 4 forms the mounting surface 10 by co-processing the front surfaces of the integrated cylinder head 1 and the camshaft bracket 2 even if they are separate parts, there is a step in the seal line. The seal performance is not deteriorated, and the seal line is formed by a surface orthogonal to the engine longitudinal direction. This eliminates the problem that the engine longitudinal length increases due to the seal line. Can be shortened.

  In particular, the tool through-hole 37 formed when the journal support portion of the control shaft 62 of the intake variable valve mechanism 6 is processed is not used as the journal support portion of the control shaft 62. Since it functions as a guide to hold, the processing accuracy of the control shaft journal support portion can be improved. Even if the lubricating oil on the head leaks from the through hole 37, it flows into the front cover 4 and therefore does not leak outside the engine.

  The tool through hole 37 formed when the journal support portion of the control shaft 62 of the intake variable valve mechanism 6 is machined includes an exhaust camshaft including sprockets 31, 33, 72 around which timing chains 34, 36 are wound. 5 and the journal of the drive shaft 52 of the intake variable valve mechanism 6. For this reason, the input generated by the tension of the timing chain 34, 36, etc. wound around these shafts mainly acts on the lower side of the journal, and in comparison with the case where the tool through hole is provided here, the tool is on the upper side. Installation of the through hole 37 is advantageous in strength.

  Similarly, the tool through-hole 37 is arranged outside the journal of the exhaust camshaft 5 and the drive shaft 52 of the intake variable valve mechanism 6 including the sprockets 31, 33, 72 around which the timing chains 34, 36 are wound. Has been. Since the chain tensioner 35 provided for securing the tension of the timing chain 34 wound around the sprockets 31 and 33 is usually disposed between the sprockets 31 and 33, the tool through hole 37 is provided. Is provided outside the two journals, so that the arrangement layout of the chain tensioner 35 is not restricted. In addition, since the input generated by the tension of the timing ring 34 or the like acts in the direction in which the journals are brought closer to each other, the provision of the tool through hole 37 on the outer side of both the journals is compared to the case where the journals are arranged on the inner side of both journals. Therefore, it is advantageous in terms of strength.

  In the case where the chain tensioner 35 is not disposed between the exhaust camshaft 5 having the sprockets 31, 33, and 72 around which the timing chains 34 and 36 are wound and the journal of the drive shaft 52 of the intake variable valve mechanism 6. As shown in FIG. 8, the tool through hole 37 for the control shaft 62 and the control shaft journal support is formed between the exhaust camshaft 5 and the journal of the drive shaft 52 of the intake variable valve mechanism 6 (inside It can also be arranged to be located in As described above, when the tool through hole 37 is positioned between the exhaust camshaft 5 and the journals of the drive shaft 52 of the intake variable valve mechanism 6 (inside), the tool through hole 37 is accommodated as shown in FIG. Thus, the joint surface 10 to be joined to the front cover formed by the greatly expanded line can be formed by a line close to the drive shaft journal in the intake variable valve mechanism 6. For this reason, the amount of overhang (deviation from the line) of the joint surface 10 with respect to the line connecting the fixing screw holes of the front cover 4 can be reduced, and the seal surface pressure at the time of joining with the front cover 4 is increased and sealed. Performance can be improved.

  In the present embodiment, the following effects can be achieved.

  (A) A frame portion 21 that overlaps with the frame portion 11 that is formed to protrude from the outer peripheral portion of the upper surface of the cylinder head 1 and a plurality of bracket portions 22 that connect the opposing frame portions 21 in a ladder shape are integrally formed. A journal support portion for the exhaust camshaft 5 and the drive shaft 52 of the intake variable valve mechanism 6 is formed between the plurality of bracket portions 22 and the front and rear frame portions 21 parallel to the bracket portions 22 and the cylinder head 1. The camshaft bracket 2, the front cover 4 which is joined to the camshaft bracket 2 and the front surface of the cylinder head 1 and accommodates the cam sprockets 31, 33, 72 and the timing chains 34, 36 or the timing belt, and the camshaft bracket And a rocker cover 3 covering the upper surface opening of the cylinder head. The frame portion 21 to which the front cover 4 of the camshaft bracket 2 is joined forms a hole 37 through which a tool for machining the journal support portion of the control shaft 62 in the intake variable valve mechanism 6 is passed. Prepare.

  Therefore, the hole 37 through which the tool is formed in the frame portion 21 of the camshaft bracket 2 holds and guides the processing tool when the journal support portion of the control shaft 62 of the intake variable valve mechanism 6 is processed. As a result, the processing accuracy of the control shaft journal support portion can be improved. Further, even if the lubricating oil on the head leaks from the through hole 37, it flows into the front cover 4 and therefore does not leak outside the engine.

  (A) The hole 37 through which the tool formed in the frame portion 21 penetrates avoids the lower portion where the load due to the tension of the timing chain 36 acts, and the drive shaft journal support portion and the exhaust cam of the intake variable valve mechanism 6 It is advantageous in terms of strength by being arranged on the upper side of the journal support portion for the shaft that is away from the cylinder head 1.

  (C) The hole 37 that penetrates the tool formed in the frame portion 21 is disposed outside the region sandwiched between the drive shaft journal support portion and the exhaust camshaft journal support portion of the intake variable valve mechanism 6. Thus, there is no interference with the chain tensioner 35 provided in the inner region in order to secure the tension of the timing chain 34 wound around both the sprockets 31, 33, and the inner side where the load due to the tension of the timing chain 34 acts. Since it is not a region, it is advantageous in terms of strength.

  (D) As shown in FIG. 8, a region where the hole 37 through which the tool formed in the frame portion 21 passes is sandwiched between the drive shaft journal support portion and the exhaust camshaft journal support portion of the intake variable valve mechanism 6. In this case, the joint surface 10 to be joined to the front cover 4 can be placed close to the journal support portion, and the overhang can be reduced to increase the seal surface pressure and improve the sealing performance.

The side view of the cylinder head structure which shows one Embodiment of this invention. The top view of a cylinder head structure similarly. The front view of a cylinder head structure similarly. The side view which shows the attachment state of a front cover. The perspective view of the camshaft bracket and cylinder head in a cylinder head structure. The principal part expansion perspective view in FIG. The block diagram of an intake variable valve mechanism. The front view of the cylinder head structure of 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Camshaft bracket 3 Rocker cover 4 Front cover 5 Exhaust camshaft 6 Intake variable valve mechanism 11, 21 Frame part 12 Rib 13, 23, 23A, 23B Journal support part 22, 22A Bracket part 24 Bearing cap 25 Fixed Bolt 26, 27A Arch surface, seal line 27 Housing 31, 33, 72 Sprocket 32 Drum case 34, 36 Timing chain 35 Chain tensioner 37 Tool through hole, tool through hole 52 Drive shaft

Claims (4)

A frame portion overlapped with a frame portion formed on the outer peripheral portion of the upper surface of the cylinder head and a plurality of bracket portions connecting the opposing frame portions in a ladder shape are integrally formed, and are parallel to the plurality of bracket portions and the bracket portion. A camshaft bracket that constitutes a journal support portion for the drive shaft of the exhaust camshaft and the intake variable valve mechanism, between the front and rear frame portions facing each other and the cylinder head;
A front cover that is joined to the camshaft bracket and the front surface of the cylinder head and houses a cam sprocket and a timing chain or a timing belt, and a cylinder head structure comprising:
The formed front cover of the camshaft bracket over the outer periphery entire circumference of the tool to hold the tool for applying a plurality of hole drilling on the same axis in the frame portion joined, the hole through which the said tool A cylinder head structure characterized by comprising:   The hole formed in the frame for allowing the tool to pass therethrough is disposed on the side away from the cylinder head of the drive shaft journal support part and the exhaust camshaft journal support part of the intake variable valve mechanism. The cylinder head structure according to claim 1.   The hole that penetrates the tool formed in the frame portion is arranged outside a region sandwiched between the drive shaft journal support portion and the exhaust camshaft journal support portion of the intake variable valve mechanism. The cylinder head structure according to claim 1 or claim 2.   The hole formed in the frame portion through which the tool passes is disposed in a region sandwiched between a drive shaft journal support portion and an exhaust camshaft journal support portion of an intake variable valve mechanism. The cylinder head structure according to claim 1 or 2.