1. Field of the Invention:
The present invention relates to a chain which is wound around a V-pulley and is suitably used for a continuously variable transmission of an automobile or other transmissions in general.
2. Related Art:
In recent years, a continuously variable transmission system comprising a pair of V-pulleys and an endless belt or chain has come to be used for a continuously variable transmission which is coupled with an engine of such as an automobile having a relatively large torque. Specifically, this continuously variable transmission system is arranged as follows. A pair of V-pulleys in which an interval between their inner walls can be varied are mounted on a drive shaft and a driven shaft, respectively, an endless belt or chain is trained between the two V-pulleys, and the interval between the inner walls of each V-pulley is varied by, for instance, hydraulic means in response to speed change commands. This causes the winding radius of the endless belt or chain trained between the V-pulleys to be varied relatively and continuously, thereby effecting a continuously variable transmission between the drive shaft and the driven shaft.
An endless belt described above is disclosed in Japanese Pat. Publication No. 6783/1980. This is a metal V-belt which is arranged such that metal blocks with a thickness of about 2 mm each having a surface of contact with an inner wall of a V-pulley are fitted with practically no gap with a hoop formed by superposing a plurality of thin metal sheets with no gap therebetween. The transmission of a driving force in this V-belt is effected as follows: The torque of the drive shaft-side V-pulley is transmitted to the blocks via a frictional force, and the driving force between the blocks is transmitted to the preceding blocks through a pushing force. Meanwhile, the driving force at the driven shaft-side V-pulley is converted again to torque through a frictional force. That is, the driving force does not substantially act on the hoop, and the hoop serves as a binding member for preventing the blocks from becoming separated. Accordingly, with this V-belt, no fracture of the hoop takes place, and it has been considered that it excels in terms of durability and noise. However, since the driving force is transmitted by the pushing force exerted among the blocks, the V-belt on the driven shaft-side V-pulley acts to escape in the direction of the outer periphery of the V-pulley. Consequently, there has been a drawback in that the friction between the V-belt and the V-pulley is made disadvantageously small, thereby causing a decline in the driving force-transmitting capabilities. In addition, it has been very difficult to fabricate a hoop formed by superposing a plurality of thin metal sheets without leaving any gap therebetween, and much manpower and time have been required in the fabrication thereof.
Accordingly, a chain for a V-pulley has been proposed in which blocks coming into contact with the V-pulley are fixedly secured to an ordinary chain. According to this chain for a V-pulley, since the driving force is transmitted through a pulling force of the chain, it is possible to overcome the problem of a decline in the driving force transmitting capabilities, which is the drawback of the above-described V-belt. Such chains for V-pulleys are disclosed in, for instance, Japanese Pat. Laid-Open Nos. 226729/1984, 226730/1984, 26831/1985, and 143243/1985. However, these prior arts are generally concerned with techniques for attaching blocks to the chain, or forming the blocks on the link plates or on the opposite ends of the connecting pins. Thus, the end faces of the blocks which are brought into contact with the inner wall of V-pulley have generally been formed into flat surfaces with no particular concern being paid to the configuration of the end faces of the blocks.
As an example in which the configuration of the end face of the block is made not flat, it is possible to cite a technique disclosed in, for instance, Japanese Utility Model Laid-Open No. 196850/1988. In this technique, a cylindrical body having an axis in the longitudinal direction of a chain abuts at a peripheral surface thereof against an inner wall of a V-pulley. However, the inner wall of the V-pulley is conically shaped, and, with this technique, the blocks and the V-pulley can theoretically be only brought into point contact with each other, so that it is considered that it is disadvantageous in terms of the driving force-transmitting capabilities.
In this respect, if the end face of the block is formed with a flat surface having the same inclination as that of the inner wall of the V-pulley (i.e., half the apex angle), it is possible for the end face of the block and the inner wall of the V-pulley to be theoretically brought into contact with each other at a linear line of contact, and this arrangement is advantageous in the transmission of the driving force- However, when the block starts to be engaged with the V-pulley, the block is brought into contact with the V-pulley at a front edge thereof, and when it begins to be disengaged with the V-pulley, the block is brought into contact with the V-pulley at a rear edge thereof. In other words, at the beginning of engagement and disengagement, the block and the V-pulley are not brought into smooth linear contact with each other and the block comes into contact with the V-pulley at its edge, thereby causing a decline in the driving force-transmitting capabilities. In addition, during a period from the time when the block enters the V-pulley and is engaged therewith and until the block is disengaged therefrom, the block rotates back and forth about an axis parallel to the axis of the connecting pin. Since this rotation of the block is effected under high pressure, rotational friction occurs between the block and the V-pulley, causing abrasion of both the block and the V-pulley and a loss in the driving force- In addition, since the portion of the end face of the block which becomes worn is fixed, it is impossible to obtain a chain for a V-pulley having an extended life. Furthermore, since the chain disposed between the two V-pulleys vibrates in the axial direction of the connecting pin, the block collides against the inner wall of the V-pulley at the time of entering the V-pulley, thereby generating noises due to this collision.
To solve these problems, the present inventors proposed a technique (Japanese Pat. Laid-Open No. 219937/1988) in which the block is connected to the tip of the connecting pin in the form of a universal joint without the block being fixed to the link plate, and the end face of the block is made rotatable and swingable to a certain degree about the axis of the connecting pin while maintaining the same inclination as that of the inner wall of the V-pulley. According to this technique, the block is rotatable, the rotational friction caused by the rotation of the block occurring at the time of entrance into the V-pulley does not occur, and the block is swingable. Therefore, it had been expected that the colliding sound occurring when the block collides against the inner wall of the V-pulley during entrance into the V-pulley would be reduced. However, it was not possible to attain a reduction of the noises to the extent that had been expected. As the reason for this problem, it can be conjectured that since the end face of the block was formed into a flat surface, the block and the V-pulley could not maintain smooth linear contact.