JPS6244186Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an auto tensioner suitable for a timing belt connecting a crankshaft and a camshaft of an internal combustion engine.

Timing belts are subject to tension changes due to engine temperature changes, belt conformation, and wear, which can cause problems such as belt noise and belt skipping. Therefore, various autotensioners have been devised for controlling the tension of the timing belt. Among these, a hydraulic damper type is known, which consists of a piston and a cylinder, and has oil sealed inside. The piston is provided with orifices that communicate with oil chambers formed on both sides of the piston. Changes in belt tension cause the piston and cylinder to displace against the spring, and this movement is regulated by the oil throttling effect of the orifice and, with appropriate braking, follows the change in belt tension. In this case, in order to prevent the volume of the oil chamber as a whole from changing even if the piston moves, the piston is provided with piston rods on the left and right sides thereof, and is structured to fit into the respective cylinder end walls. In this way, by keeping the volume of the oil chamber in the cylinder constant when the piston moves, it is possible to suppress the occurrence of oil pressure changes that would cause resistance to the movement of the piston. However, due to the machining accuracy of the piston, it is actually difficult to keep the volume change from occurring over the entire stroke of the piston. In this case, it will not be possible to respond sufficiently to changes in belt tension.

In view of the drawbacks of the conventional technology, the U.S. Pat.
The publication discloses a cylinder equipped with a free piston to prevent changes in the oil chamber volume within the cylinder. These smooth operations are realized by moving the free piston to follow the relative movement between the piston and the cylinder. However, this prior art relates to an autotensioner for a chain for two-wheeled vehicles, and in the case of a chain, it is not necessary to consider shrinkage, but only elongation, so a check valve is provided on the piston, and the piston It is applied only in the direction in which the chain is stretched (that is, in the direction in which the chain is stretched). However, since the timing belt that is the subject of this application not only expands but also contracts, this prior art cannot be applied as is.

Therefore, an object of the present invention is to provide an autotensioner suitable for a timing belt. To achieve this purpose, the autotensioner of the present invention has a cylinder and a piston that slides inside the cylinder, one of which is attached to the engine body, and the other is an idler that contacts the belt. A spring means is provided for urging the idler to constantly contact the belt, and a first oil chamber is formed on one side of the piston in the cylinder, and a second oil chamber is formed on the other side of the piston. The second oil chamber is communicated with each other by an orifice formed in the piston, and is provided with means for absorbing a change in volume of the oil chamber in the cylinder when the piston and cylinder move relative to each other.

The present invention will be explained below with reference to the drawings. In FIG. 1, 10 is a timing pulley on a crankshaft, 12 is a timing pulley on a camshaft, and these are interconnected by a timing belt 14.
16 is a tension roller, one end of which is rotatably attached to the tension bar 10 around a pin 18. A belt tensioner 24 is provided between the other end of the lever 20 and the engine body 22.

In the first embodiment, the belt tensioner 24 has a configuration as shown in FIG. A piston 28 is slidably fitted into the cylinder 26, and the piston rod 3
0 is inserted into the end wall of the cylinder 26 through a seal 32 and connected to the tension lever 20 of FIG. connected to. (Contrary to this, the piston rod 30 can be connected to the engine body 22 and the bracket 34 to the tension lever 20.) The spring 40 contacts the piston 28, and the tension roller 16 contacts the timing belt 14. A force is applied to the lever 20 to bring it into contact. Inside the cylinder 26, a first oil chamber 42 and a second oil chamber 44 are formed on one side of the piston 28 and on the other side, which are filled with oil and communicated with each other via an orifice 46. A free piston 48 is fitted into the cylinder 26 via a seal 50, and the free piston 48 forms a wall surface of the second oil chamber 44 facing the piston 28. A cap 52 is fitted into the cylinder 26, and an atmospheric chamber 5 between the cap 52 and the free piston 48
6 communicates with the atmosphere through holes 58.

In the above configuration, when the belt 14 stretches (because the shrinkage of the cylinder block or cylinder head due to temperature change is larger than the belt deformation and the belt stretches outward), the force of the spring 40 causes the piston 28 to move as shown in FIG. On the other hand, as the belt 14 contracts, the piston 28 moves to the left in FIG. 2 against the force of the spring 40. Following the left and right movement of the piston, the free piston 48 moves left and right due to changes in oil pressure, keeping the volume of the entire oil chamber constant, and as a result, the volume between the first oil chamber and the second oil chamber is increased. Differences in volume, including those due to processing accuracy, are absorbed,
Piston 2 due to gradual changes in belt tension.
8 smooth movements are realized. Also piston 28
The speed of the piston 28 is appropriately regulated by the resistance force as the oil passes through the orifice 46 in the belt, and belt flapping during engine operation can be eliminated by appropriately selecting its dimensions.

In the embodiment of FIG. 3, the free piston 4 of FIG.
8 is replaced by a bellows 60. The open end 60A of the bellows 60 is restrained by the cap 52 so as not to move, and the closed end 60B forms a wall surface of the second oil chamber 44 facing the piston 28.

Following the left and right movement of the piston 28, the bellows 60 expands and contracts, thereby keeping the volume of the entire oil chamber constant. Therefore, the volume difference is absorbed.

In the embodiment of FIG. 4, the volume difference absorption means is formed as a rubber bag 70. In the embodiment of FIG. A suitable amount of air is sealed in the rubber bag. Following the movement of the piston 28, the rubber bag expands and contracts, absorbing the difference in cross-sectional area, and realizing smooth movement of the piston 28.

As described above, in the present invention, by providing only an orifice on the piston and providing a volume difference absorbing means composed of a free piston, bellows, or rubber bag, it is possible to effectively work on both expansion and contraction of the dajiming belt. .

[Brief explanation of the drawing]

Figure 1 is a front view of the engine body equipped with the belt tensioner of the present invention, Figure 2 is a sectional view showing the first embodiment of the belt tensioner of the present invention, and Figures 3 and 4 are FIG. 2 is a diagram similar to FIG. 2 showing different embodiments; 10, 12...Timing pulley, 14...Timing belt, 16...Idler, 24...Belt tensioner, 26...Cylinder, 28...Piston, 40...Spring, 42...First oil chamber, 44
...Second oil chamber, 48...Free piston, 60...
...Bellows, 70...Rubber bag.

Claims (1)

[Scope of utility model registration request] An autotensioner for applying tension to a timing belt wound between a driving timing pulley and a driven timing pulley, and includes a cylinder and a piston that slides inside the cylinder. One of the cylinder and the piston is attached to the engine body side, and the other is connected to an idler that abuts the belt, and a spring means is provided to always bias the idler to abut the belt. The second oil chamber is located on the other side of the first oil chamber.
An oil chamber is formed, and the connection between the first oil chamber and the second oil chamber is established only by an orifice formed in the piston without intervening a check valve. An autotensioner for a timing belt that communicates with each other regardless of direction and is equipped with means for absorbing changes in volume of an oil chamber in a cylinder when a piston and a cylinder move relative to each other.