JPS58203264A - Tooth shape of sprocket - Google Patents

Abstract

PURPOSE:To effectively reduce the creation of noises at a working time, by enlarging radius R of the circular arc of the tooth base of a sprocket, compared with the radius of a roller chain or the radius (r) of the bush of a bush chain. CONSTITUTION:A drawing shows a condition in which a roller 7b in a timing chain 7 just set in a space between adjoining teeth of a sprocket 4, and the centers of the rollers 7a and 7b are positioned on a pitch circle P. Where the sprocket 4 turns by theta=pi/Z from said condition, the roller 7b is smoothly displaced from the initial entrance level H1 to a level H2 along the circular arc 4a of a tooth base. If, subsequently, the sprocket 4 turns by theta=pi/Z, the roller 7b smoothly moves to the maximum engaging point 02 from a point 01 along the circular arc 4a, and this eliminates the possibility of hammering noises created between the roller 7b and the sprocket 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applied to a sprocket tooth shape for reducing the engagement between a chain and a sprocket, and particularly to a drive mechanism for intake and exhaust valves for four-cycle gasoline engines. Winding is related to the shape of the teeth of the sprocket.A belt or lobe transmission device transmits power through friction, whereas a chain transmission device transmits power through the meshing relationship between the chain and the sprocket. Therefore, the rotation of the driving sprocket and the driven sprocket can be reliably transmitted without causing slippage.

However, in a one-chain transmission device, generation of vibration and noise is unavoidable due to its structure, and how to reduce these is a major technical issue.

One of the causes of noise is chain vibration. That is, when the roller 02 of the roller chain is caught in the sprocket 01 as shown in FIG. 1, the entry level of the roller chain is at Hl. After this, when the sprocket 01 rotates by θ"-π/2, the roller 02 reaches the H2 level, which is deviated from the level H7 by ΔH, as shown in FIG. 2. At this time, the entry level of the roller chain is H2. This △H can be found using the following formula (where dp is the pitch diameter of sprocket 01, and 2 is the number of teeth on the sprocket). Therefore, the △H is the amplitude △H when approaching the sprocket. It can be said that it vibrates at /2.

However, the state shown in Fig. 2 is an ideal meshing state in which the roller center and the sprocket pitch circle are aligned, and in reality, the roller o2 is in the position shown in Fig. 2 and is not subject to a force that displaces it in the level H1 direction. As shown in Fig. 3, it is located slightly outward from the pitch circle. At this time, the roller 02 is referred to as the "biting start point" with respect to the roller center last prokerato 01. Further, when the sprocket 01 rotates by θ=π/Z from the state shown in FIG. 3, the meshing relationship between the sprocket 01 and the roller 02 returns to the state shown in FIG. The center of the roller at this time is referred to as the "maximum biting point" of the roller 02 relative to the sprocket.

In short, as sprocket) 01 rotates, roller 0
2 is displaced from the "biting start point" to the "maximum biting point", and this displacement causes roller 02 to move to sprocket 0.
The bottom of tooth No. 1 is struck, producing a hammering sound.

Overhead Radcam type 4-cycle driven by Chaseo.
In engines, a rubber material is sometimes baked onto the cam sprocket in order to suppress this hammering noise, but it was difficult to use this method because the timing sprocket on the crankshaft side required durability. . The tooth ratio between the cam sprocket and timing sprocket is 2:1.
Since the timing sprocket has a small number of teeth (2), the above-mentioned ΔH is large, and countermeasures against hitting noise are required.

Another cause of noise generation is that the chain speed changes periodically. In other words, since a chain is made up of many links, it can be bent freely as a whole, but since each link does not bend, it forms a polygon when meshed with a sprocket. Therefore, the situation is the same as when a belt is attached to a polygonal wheel, and the radius changes periodically, and the chain speed changes periodically accordingly. This change is
When the maximum chain speed is v max and the minimum chain speed is v min, the following equation holds.

(However, dp is the pitch circle diameter, 2 is the number of teeth of the sprocket, and ω is the angular velocity of the sprocket.) In this way, since the chain speed changes between v max and v min, meshing noise will inevitably occur. will occur.

The meshing noise caused by the change in chain speed in the latter case is 1
Although it cannot be avoided in the chain transmission structure, the noise caused by vibration in the former can be appropriately suppressed by structural innovation. It is characterized in that the radius R of the sprocket tooth bottom arc is larger than the roller radius of the roller chain or the bush radius r of the bush chain.

Hereinafter, a case will be described in which the present invention is applied to driving an overhead cam in a V-type four-cycle engine for a motorcycle.

A pair of camshafts 5 are supported within the cylinder head 2 of the engine 1, and a timing chain ( A roller chain) 7 is stretched (see Fig. 4).

Therefore, the timing sprocket 4 is formed so as to satisfy the equation (1) below.

(However, d is the pitch FJ of timing sprocket 4.
is the diameter) In the above configuration, during enrun driving, the rotation of the crankshaft 3 is transmitted to the timing sprocket 4, the timing chain 7, the cam sprocket 6, and the camshaft 5, and the pulp 8 is operated.

At this time, the timing subbutton 4 and the timing chain 47 are engaged as shown in FIGS. 5 to 7.

FIG. 5 shows a state in which the timing chain 7 has the ocher roller 7b caught between the teeth of the sprocket 4 by J degrees, and the return center of each roller 7a, 7b is located on the pitch circle P. When the sprocket 4 rotates by θ:π/Z from this state, the roller 7b is smoothly displaced from the first approach level H5 of 11 to the level H2 along the tooth bottom arc 4a. At this time, the center of roller 7b is the starting point of I7 biting.
01, and O1 is located slightly outward from the pitch circle P.

When the sprocket 4 continues to rotate by θ=π/2, the state shown in FIG. 5 is reached. Therefore, the roller 7b is at point 0. From there, it will be displaced to the "maximum biting point" 02 on the pitch circle P.

The state during this time is shown in an enlarged scale in FIG. The roller 7b is
Since there is a smooth transition from the point O2 to the point 02 along the arc 4a, it is difficult for a hitting sound to occur between the roller 7b and the sprocket 4. Such an effect is obtained by the relationship of equation (1) above, and the radius t of the arc 4a is equal to the radius r of the roller 7a.
If it is equal to , no such effect will be obtained.

The tooth shape of this embodiment may be applied not only to a timing sprocket but also to a cam sprocket, and can also be applied to other roller chain or bush chain transmission devices.

As is clear from the description of the above-mentioned embodiments, in the present invention, the sprocket tooth bottom arc 'V' and the radius R are formed to be larger than the diameter of the roller of the roller chain or the bush radius r of the bush chain. Not only can the noise during operation be effectively reduced, but it can also be manufactured at a lower cost than a silent chain.

[Brief explanation of the drawing]

1 to 3 are schematic explanatory diagrams showing the operation mode of a well-known sprocket, and FIG. 5 and 6 are explanatory diagrams showing the operating mode of the sprocket, respectively, and FIG. 7 is a conceptual diagram showing the state of meshing of the rollers with the sprocket. Link shaft, 4...Timing sprocket, 5...Camshaft, 6...Cam sprocket, 7...Timing chain, 7b...Roller, 8...No(lube) Agent: Patent attorney Ehara Bogai 1 person = 43 Eup 1 Figure 2

Claims (1)

[Claims] The roller chain mata is a sprocket for a bushing chain, and is characterized in that the relationship between the radius R of the sprocket tooth bottom arc and the roller radius of the roller chain or the bushing radius r of the bushing chain is R)r. The tooth shape of Esojin's cam sprocket.