JPS648163B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a camshaft bearing structure for an OHC type (overhead camshaft type) internal combustion engine.

The camshaft of an OHC internal combustion engine is supported between a lower bearing and an upper bearing on the cylinder head side. In such an OHC internal combustion engine, cylinders are arranged in parallel,
If a common camshaft is installed between these cylinder heads and the camshaft is driven by a transmission mechanism such as a sprocket or chain installed in the middle, a space for the transmission mechanism such as a cam chain chamber is provided in the center of the cylinder head. Therefore, there is a risk that the wall thickness around the cavity of the head will be thinner and the rigidity will be relatively lowered. Further, the mating surface of the cylinder head with respect to the cylinder block is machined to be flat by a milling machine or the like. However, in this machining process, when viewed microscopically, the flat surface often becomes a concave surface approximately at the center of the cutting length.

In such cases, for example, in cylinder heads of multi-cylinder in-line engines for four-wheeled vehicles, where the cam drive section is provided at one end of the camshaft, the empty space in the cylinder head where the camshaft drive section is installed is Since the part with weak rigidity is located at one end of the cylinder head, it is necessary to tighten approximately one plate when attaching the cylinder head to the cylinder block. Sufficient rigidity is ensured, and there is almost no deformation of the cylinder head due to tightening.

However, as mentioned above, when a space is provided between the cylinders of the cylinder head for driving the cam chain, the left and right sides of the cylinder head sandwiching this space are connected by a thin rib, so in such a cylinder head, , the weak rigidity of this rib part cannot support the dents that occur during machining mentioned above,
Therefore, when the bolts are tightened, the cylinder head's weakly rigid portion (the aforementioned rib portion) near the cavity is deformed in a direction that reduces the clearance created at the mating surface below the cavity of the cylinder head. In other words, the cylinder head is deformed into an upward curvature with the hollow part for the cam chain at the bottom.

In particular, modern internal combustion engines use light alloys such as aluminum alloys due to the need for weight reduction. There is a risk that the deformation due to the tightening load will be concentrated in the low-rigidity part of the cavity, and that such deformation will spread to the lower bearing of the camshaft installed on the cylinder head, especially across the cavity. The outer part of the bearing (opposite the cavity) is deformed in the camshaft direction by tightening in the inner cylinder axial direction (in the direction that reduces the clearance of the mating surfaces of the cylinder heads mentioned above). For this reason, the camshaft is microscopically supported in an arched shape, which is undesirable.

In order to solve the above problem, increasing the wall thickness of the cylinder head to prevent such deformation has been considered, but this would increase the weight of the cylinder head and the overall weight of the internal combustion engine, leading to a demand for weight reduction. This would be contrary to the above.

The present invention has been made in order to improve the above-mentioned problems, and its object is to provide a camshaft with bearings disposed on both sides in the axial direction of a camshaft provided on a cylinder head, and a camshaft drive section mounted on the cylinder head between the bearings. In an internal combustion engine, the other side of the bearing is inclined toward the cylinder head side with respect to the cylinder block tightening side in the axial direction. It absorbs deformation in the direction that reduces the clearance of the mating surface between the cylinder block and cylinder head on this tightening side during mounting, and improves the flatness of the bearing surface in the axial direction due to the above-mentioned inclination when tightening the cylinder head to the cylinder block. The camshaft can be supported without bending the camshaft, and the above can be achieved without reinforcing the bearing or cylinder head by increasing the wall thickness or increasing the rigidity.The camshaft can be supported smoothly while reducing the weight of the cylinder head. A camshaft bearing structure for an internal combustion engine is provided.

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 is a vertical front view of an internal combustion engine, and in the example, it is a two-cylinder type with cylinders arranged side by side on the left and right, and is a DOHC engine.
It shows a type of internal combustion engine.

The internal combustion engine 1 includes two cylinder blocks 2, 2 arranged in parallel. Each block is connected and supported by a crankcase (not shown), and a piston 3 is slidably inserted into each block. Cylinder heads 4, 4 are fixed on top of the cylinder head 2, and camshafts 5 are disposed horizontally on the front and rear of the cylinder heads 4, 4. The camshafts 5 each have a sprocket 6, which is a camshaft driving member, provided at the center in the axial direction, and a sprocket 6 that is wound around the sprocket. In the figure, 8 is an upper cam holder which is a second bearing part forming the upper bearing of the camshaft, and 9 is a cylinder head cover.

The cylinder heads 4, 4 are constituted by a cylinder head block 10, the details of which are shown in FIG. 2, and the left and right cylinder heads 4, 4 are integrally cast as a block 10. The block 10 has a surrounding frame part 11 on the heads 4, 4, and the surrounding frame part 11
A space S for housing a cam chain 7 that penetrates vertically is provided between the heads 4, 4, and a space S in the center is provided between the heads 4, 4.
Heads 4 and 4 are on the left and right. Binding boss portions 12 are provided at four locations on the front and back of each outer side of the heads 4, 4, and binding boss portions 13 are provided at the front and rear of the opposing inner sides of the heads 4, 4 near the empty space S. are provided at four locations in total, and binding boss portions 14 are provided at four locations on the left and right outside of the front and rear ends of the space S, and these 12 binding boss portions 12, 13, ... are used to secure the bolt 15.
The cylinder head block 10 is screwed to the cylinder block 2 by bolts 151 and the connecting boss portion 14 is screwed to the cylinder head block 10.

In front and behind the cylinder heads 4, 4 of the cylinder head block 10, lower cam holders 16, which are first bearing parts forming the lower bearings of the camshafts, are provided on the left and right sides from the center of the cylinder heads. It has a circular concave shape, and both ends are open to the left and right, that is, in the axial direction of the camshaft 5. In addition, in the lower cam holder 16 main body, the support part 21 of the intake/exhaust valve and the lower cam holder 16 are arranged close to each other in order to shorten the width direction of the engine, and the camshaft 5 is cantilever-supported by the lower cam holder 16, so that the axial direction of the lower cam holder 16 is It requires a length of , and forms an L-shape in plan as shown in the figure. The intake/exhaust valve holding part 21... is DOHC as shown in the figure.
Since the cylinder has two cylinders with four valves per cylinder, four valves are provided in each cylinder head 4,4. At the front and back of the cylinder heads 4, 4, and outward from the center, there are storage recesses _S1 for the valve rocker arm (not shown)...
Specifically, they are provided at the four corners of the surrounding frame part 11.

The above-mentioned parts including the lower cam holder are entirely cast as one piece, and each of the lower cam holders 16 is arranged symmetrically in the axial direction, and in the embodiment, a lubricating oil groove 17 that is long in the axial direction is formed in the bottom of each of the lower cam holders 16. Holder 16...
The inner side A in the axial direction from the center of the concave surface 18 has a flat bottom in the axial direction, and the outer side B in the axial direction from the center has a flat bottom in the cylinder head 4.
direction, that is, tilt C downward. The amount of inclination is made approximately equal to the amount of deformation of the cylinder head block 10 when it is connected, and the outer end _B1 of the outer side B is lowered in the axial direction with respect to the inner side A by about 25μ with respect to the extension line of the inner side A. It is tilted from the center, and the tilt angle θ is determined as appropriate.

In the figure, reference numeral 19 denotes a chain tensioner, which is fixed to boss portions 20 provided on the left and right sides of the intermediate portions of the cylinder heads 4, 4 in the longitudinal direction.

Between the left and right lower cam holders 16, that is, 1
The camshaft 5 is horizontally suspended between 6-1 and 16-2, 16-3 and 16-4, and the Atsupaka cam holder 8 is placed and fastened on each cam holder, so that the camshaft 5 horizontally suspended front and rear can be freely rotated. To support. The Atsupaka cam holder 8 connects the camshaft 5 to the lower cam holder 16.
Since the camshaft is supported in a cantilever manner, the upper surface of the camshaft is supported in order to receive the reaction force due to opening and closing of the intake and exhaust valves, and a support 81 is formed integrally with the upper cam holder 8 and extends in the axial direction. In addition, 22 in the figure is a lubricating oil retaining groove formed on the bearing concave surface of the Atsupaka cam holder.
23 is an oil passage provided in the camshaft, 24 is a bolt for mounting the cylinder head cover 9, and 25 is a rocker arm shaft.

Next, to explain the function and effect in detail, the boss portion 13
Since it is connected to the cylinder block with bolts 15..., 151 via..., 14..., the inner side A of the planar L-shaped holder 16 is tightened on both sides to connect the cylinder block 2 and cylinder heads 4, 4. is pressed downward, which is the direction that reduces the clearance between the mating surfaces, while the outside B is far from the binding part,
Also, there is a recess _S1 on this side, which deforms slightly upward because it is not directly connected to the cylinder block side with a bolt.This upward deformation is caused by the downwardly inclined surface C formed on the outside. When the cylinder head block 10 is assembled, the outside B becomes a flat surface where the inside A and its bottom are continuous in the axial direction.
Therefore, due to the upward deformation of the outside, the camshaft 7
No load will be applied to cause the camshaft 7 to deform into an upward arch, and the camshaft 7 will be supported by the lower cam holder which is flat in the axial direction. Therefore, smooth rotation of the camshaft is ensured, and uneven wear of the bearing and camshaft is prevented. In the above, we took advantage of the deformation of the cylinder head block when it was connected, and in anticipation of this, we provided an inclined part in the lower cam holder and corrected it by the deformation of the inclined part. There is no need to increase the strength and rigidity by increasing the wall thickness of the head, and the cylinder head can be designed to be thinner without increasing its weight, making it possible to reduce the weight of the cylinder head, thereby reducing the weight of the internal combustion engine. The above can be achieved with a simple configuration of forming an inclined portion.

The present invention has many advantages as described above.

In the embodiment, the present invention is applied to a DOHC or OHC type internal combustion engine, but the type may be arbitrary, and the present invention can also be applied to a single cylinder type internal combustion engine.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a longitudinal sectional front view of an internal combustion engine, and FIG.
FIG. 3 is an enlarged sectional view of the bearing portion, and FIG. 4 is a longitudinal sectional side view of the main part of the bolted joint. In the drawing, 4 is a cylinder head, 5 is a camshaft, 8 and 16 are bearings, C is an inclined surface, and 13 and 14 are connecting portions.

Claims (1)

[Claims] 1. A camshaft first bearing part provided in the cylinder head and a separate second bearing part coated thereon cooperate to constitute a camshaft bearing, and the bearings are arranged on both sides of the camshaft in the axial direction. A space is formed between the first bearing portions of the cylinder head to support the camshaft, and a space is formed between the first bearing portions of the cylinder head, and the cylinder is connected to the cylinder block at an axially inward portion of the first bearing portion sandwiching the space. A camshaft for an internal combustion engine, characterized in that an axially outer side portion of the first bearing portion on the cylinder head side is formed to be inclined outward in the radial direction of the camshaft in advance. Bearing structure.