JP2744814B2 - Overhead cam engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an overhead cam engine in which rotation of a crankshaft is reduced on an intermediate shaft and then transmitted to a camshaft.

[Related Art] Recently, there has been a demand for an engine for a passenger car to reduce the engine length and the engine width as much as possible due to the restriction of the size of the engine room. For this reason, especially in the case of a so-called DOHC type engine in which two camshafts for intake and exhaust are provided in the cylinder head, the interval between these two camshafts should be made as small as possible to make the cylinder head compact. Is desired.

For this reason, conventionally, as seen in, for example, JP-A-59-74312, an intermediate shaft is provided between a camshaft and a crankshaft, and a deceleration pulley and a crank provided on the intermediate shaft are provided. 2. Description of the Related Art There is known an engine in which a shaft is interlocked via a timing belt and a driving sprocket on the intermediate shaft and a timing sprocket on a camshaft are interlocked via a timing chain.

According to this engine, since the rotation speed of the crankshaft is transmitted to the camshaft after being once reduced on the intermediate shaft, the diameter of the timing sprocket on the camshaft can be reduced. Therefore, the cylinder head can be downsized by narrowing the arrangement interval between the two camshafts, which is advantageous in suppressing the engine width to be narrow.

[Problems to be Solved by the Invention] In such a configuration, the smaller the number of teeth of the timing sprocket, the smaller the outer diameter of the sprocket, which is advantageous in reducing the size of the cylinder head.

However, if the number of teeth of the timing sprocket is determined in consideration of the downsizing of the cylinder head, the deceleration pulley and the driving pulley on the intermediate shaft may increase in diameter. There is a possibility that the swelling will be large near the axis.

For this reason, considering the reduction ratio between the camshaft and the crankshaft, there is naturally a limit to downsizing the cylinder head, and there is still room for improvement in this regard.

The present invention has been made in view of such circumstances, and it is possible to further reduce the diameter of the timing sprocket on the cam shaft without affecting peripheral components, and to reduce the size of the compact overhead cam diameter with a small cylinder head. The purpose is to provide an engine.

[Means for Solving the Problems] Therefore, in the present invention, an intermediate shaft is provided between a valve operating cam shaft provided on a cylinder head and a crankshaft, and a primary sprocket and a crankshaft on the intermediate shaft are provided. And a secondary timing chain between the secondary sprocket that rotates integrally with the primary sprocket and the timing sprocket provided on the camshaft, and intermediately rotates the crankshaft. In an overhead cam type engine which transmits a signal to a camshaft after deceleration on a shaft, the pitch of the secondary timing chain is set to be smaller than the pitch of the primary timing chain.

[Operation] According to this configuration, since the pitch of the teeth of the timing sprocket is also reduced as the pitch of the secondary timing chain is reduced, the reduction ratio between the camshaft and the intermediate shaft is significantly changed. Therefore, the outer diameter of the cam sprocket can be reduced.

Therefore, especially in an engine having two camshafts for intake and exhaust, the interval between these camshafts can be narrowed, and the cylinder head can be downsized.

Embodiment An embodiment of the present invention will be described below with reference to the drawings applied to a V-type multi-cylinder engine.

The cylinder block denoted by reference numeral 1 in the drawing is a crankshaft 2
Is provided. On the upper surface of the lower case 3, a pair of cylinders 4 are erected in a V-shape. As shown in FIG. 1, one of the cylinders 4 has a plurality of cylinders arranged side by side in the axial direction of the crankshaft 2, and is fitted on the upper surface of the cylinder row 5. It comprises a cylinder head 6 and a head cover 7, and the cylinder row 5 is integrated with the lower case 3.

A valve operating chamber 8 is formed between the cylinder head 6 and the head cover 7. The valve operating chamber 8 houses an intake camshaft 10 and an exhaust camshaft 11. These camshafts 10, 11
Are parallel to the crankshaft 2 and are arranged parallel to each other, and a timing sprocket 12 is bolted to one end of each of the camshafts 10 and 11.

The timing sprocket 12 includes a boss 13 mounted on the outer periphery of the camshafts 10 and 11, and two rows of teeth 13a protruding from the outer periphery of the boss 13, and the teeth 13a
Are arranged side by side in the axial direction.

The front surfaces of the cylinder rows 5 and one end of the cylinder head 6 are covered with a chain cover 15. These cylinder row 5, cylinder head 6 and chain cover 15
The timing sprocket 12 and the drive sprocket 9 provided at one end of the crankshaft 2 face the chain passage 16.

On the front face of the cylinder head 6 facing the chain passage 16,
The bracket 18 is bolted. A tensioner mounting portion 19 extending toward the timing sprocket 12 and an intermediate shaft 20 projecting into the chain passage 16 are integrally formed on the bracket 18. A primary sprocket 21 is rotatably supported on the outer periphery of the intermediate shaft 20. The number of teeth of the primary sprocket 21 is greater than the number of teeth of the driving sprocket 9, and a single-row primary timing chain 22 is bridged between the two sprockets 9 and 21. As shown in FIG. 4, the primary timing chain 22 includes a plurality of pins 24 rotatably supporting a roller 23, a pair of left and right roller link plates 25 and a pin link plate.
26, the tooth portions 9a and 21a of both sprockets 9, 21 mesh between the rollers 23.

On the surface of the primary sprocket 21 on the chain cover 15 side,
The secondary sprocket 27 is formed integrally. The secondary sprocket 27 has two rows of teeth 27a corresponding to the timing sprocket 12. The number of teeth of this tooth part 27a is determined by the tooth part 21a of the primary sprocket 21 and the timing sprocket 1
The number of teeth of the second tooth portion 13a is smaller than that of the second tooth portion 13a. Between the timing sprocket 12 and the secondary sprocket 27, a two-row secondary timing chain 28 is wound. As shown in FIG. 5, the secondary timing chain 28 includes a plurality of pins 29 rotatably mounted with a pair of rollers 30a and 30b, and a bush link plate 31 and a pin link plate 32 for each row of the rollers 30a and 30b. And a bush link plate 3 located between the rollers 30a and 30b.
1 are connected by an intermediate link plate 33, and between these two rows of rollers 30a and 30b, the teeth 27a of the secondary sprocket 27 and the teeth 13a of the timing sprocket 12 mesh.

Therefore, the rotational speed of the crankshaft 2 is reduced in two steps between the crankshaft 2 and the intermediate shaft 20 and between the intermediate shaft 20 and the camshafts 10 and 11, and then the camshafts 10 and 11
Is transmitted to

Then, as shown in FIG. 2, the pitch P ₂ of the secondary timing chain 28 is set smaller than the pitch P ₁ of the primary timing chain 22, the pitch P only ₂ small amount, timing sprocket 12 Also, the pitch of the teeth 13a, 27a of the secondary sprocket 27 is small.

A tensioner 35 for adjusting the tension of the secondary timing chain 28 is attached to the tensioner mounting portion 19 of the bracket 18, and a tensioner 36 for adjusting the tension of the primary timing chain 22 is connected to one end of the cylinder row 5. It is bolted to the front.

According to this configuration, the pitch P ₂ of the secondary timing chain 28 that transmits the rotation of the secondary sprocket 27 to the camshafts 10 and 11 is set to the primary timing chain 22 on the crankshaft 2 side.
Having set smaller than the pitch P ₁ of the pitch of the teeth 13a of the timing sprocket 12 secondary timing chain 28 meshes also reduced.

Therefore, the outer diameter of the timing sprocket 12 can be reduced without greatly changing the reduction ratio between the camshafts 10, 11 and the intermediate shaft 20, and the two camshafts 1
The cylinder head 6 can be miniaturized by narrowing the arrangement intervals of 0 and 11.

In the present embodiment, the secondary timing chain
Because the 28 is a two-row type, this secondary timing chain 28
Despite the reduced pitch P ₂ of, it is possible to sufficiently ensure the strength of the secondary timing chain 28, it can be reliably transmitted to the camshaft 10, 11 the rotation of the secondary sprocket 27.

In the above embodiment, the intermediate shaft is provided on the cylinder head side, but may be provided on the front surface of one end of a cylinder row to which this cylinder head is connected.

Further, in the above-described embodiment, the secondary timing chain is arranged on the front side of the chain cover side of the primary timing chain. However, the primary timing chain may be arranged in front of the secondary timing chain.

Further, the overhead cam type engine according to the present invention is not limited to the V-type engine having the cylinder arrangement of the V-type,
For example, it may be an in-line multi-cylinder engine, and the camshaft is not limited to one having two intake and exhaust cams, but a so-called SOHC having one intake cam and one exhaust cam on one camshaft. It may be a shaped engine.

[Effects of the Invention] According to the present invention described in detail above, the pitch of the secondary timing chain is made smaller than the pitch of the primary timing chain. Therefore, the pitch of the teeth of the timing sprocket with which the secondary timing chain meshes is also made small. Thus, the outer diameter of the timing sprocket can be reduced without greatly changing the reduction ratio between the cam shaft and the intermediate shaft. Therefore, the cylinder head can be reduced in size accordingly, and a compact and well-organized engine can be provided.

[Brief description of the drawings]

Drawings show an embodiment of the present invention, FIG. 1 is a front view in which a drive system path of a cam shaft is partially sectioned, FIG. 2 is a front view showing a winding state of a primary timing chain and a secondary timing chain, FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 1, FIG. 4 is a front view of the primary timing chain partially sectioned, and FIG. 5 is a front view of the primary timing chain partially sectioned. 2 ... Crank shaft, 6 ... Cylinder head, 10,11 ...
Cam shaft, 12 timing sprocket, 20 intermediate shaft, 21 primary sprocket, 22 primary timing chain, 27 secondary sprocket, 28 secondary timing chain.

Claims (1)

(57) [Claims] An intermediate shaft is provided between a crankshaft and a valve operating cam shaft provided on a cylinder head, and a primary timing chain is bridged between a primary sprocket and the crankshaft on the intermediate shaft. A secondary timing chain is bridged between a secondary sprocket that rotates integrally with the primary sprocket and a timing sprocket provided on the camshaft, and the rotation of the crankshaft is reduced on an intermediate shaft and transmitted to the camshaft. An overhead cam engine as described above, wherein the pitch of the secondary timing chain is set smaller than the pitch of the primary timing chain.