Chain Tensioner

The present invention relates to a chain tensioner.

Different types of chain tensioners have been proposed for providing the adequate tension to a chain. One of such chain tensioners is disclosed, for example, in JP-B2 No. 60-527, published on Jan. 8, 1985 in Japan.

JP-B2 No. 60-527 discloses a chain tensioner as shown in FIG. 6. Referring to FIG. 6, an engine cylinder block 64 is formed with a through bore 65. The chain tensioner includes a body 63 received in the bore 65 from the outside of an engine, a plunger 61 which is slidably received in the body 63, and a spring 62 for biasing the plunger 61 in such a direction as to protrude from the body 63.

An end portion of the plunger 61 protrudes inside the engine so as to press a chain (not shown)through a slide member (not shown). The tension of the chain is adjusted to an appropriate value by a force of spring 62.

JP-B2 No. 58-17891 discloses a chain tensioner. This chain tensioner comprises a body formed with a cylindrical bore having one end closed, and a plunger slidably received in the cylindrical bore. The plunger defines within the cylindrical bore a variable volume chamber. The body is formed with a recess serving as on oil reservoir. The body is provided with a one-way passage which allows a one-way flow of oil from the oil reservoir to the variable volume chamber. A flow restrictor is mounted in a passage formed through the body to restrict flow of oil from said variable volume chamber to the oil reservior. The oil within the oil reservoir is subject to atmospheric pressure. A spring is disposed within the body to bias the plunger in a direction to protrude from the body.

A problem encountered in the chain tensioner disclosed in JP-B2 No. 60-527 is that noise due to vibration of the chain is produced in expanding and contracting the spring 62 when the tension of the chain periodically varies with the variation of engine speed.

Another problem encountered in the chain tensioner disclosed in JP-B2 No. 58-17891 is although noise due to vibration of the chain is restrained by the presence of the oil reservoir, a restraint of noise is not sufficient that if the oil reservoir is small in capacity. On the other hand, in order to obtain sufficient restraint of noise, the oil reservoir should be larger, resulting in increase in size of the chain tensioner and/or difficulty to find a space or area for the oil reservoir.

It is, therefore, an object of the present invention to provide an arrangement wherein an oil reservoir of a chain tensioner is provided without any increase in size nor any substantial structural modification on an engine component part to which the chain tensioner is to be attached.

There is provided according to the present invention, an engine comprising:

a chain tensioner body formed with a cylindrical bore having one end closed;

a plunger slidably received in said cylindrical bore, said plunger defining within said cylindrical bore a variable volume chamber;

means for defining an oil reservoir;

one-way passage means for allowing a one-way flow of oil from said oil reservoir to said variable volume chamber, but preventing the reverse flow;

said oil reservoir defining means including,

a predetermined engine component part with a mounting site;

said chain tensioner body cooperating with said predetermined engine component at said mounting site to define therebetween said oil reservoir.

FIG. 1 is a front view, partly in section, illustrating an internal combustion engine to which a preferred embodiment of a chain tensioner according to the present invention is applied,

FIG. 2 is a perspective view illustrating a cylinder head with the chain tensioner detached,

FIG. 3 is an enlarged detail illustrating the chain tensioner shown in FIG. 1,

FIG. 4 is a longitudinal section illustrating the chain tensioner,

FIG. 5 is a view similar to FIG. 4, taken along the line A--A of FIG. 4, and

FIG. 6 is a view similar to FIG. 4, illustrating a conventionally proposed chain tensioner.

Referring to the accompanying drawings, a preferred embodiment of a chain tensioner according the present invention will be described.

Referring to FIG. 1, an internal combustion engine 1 includes a cylinder clock 10, and a cylinder head 11 disposed thereon. A crankshaft is rotatably mounted to the cylinder block 10, whereas a camshaft is rotatably mounted to the cylinder head 11. A crank sprocket 2 is coupled with the crankshaft, whereas a cam sprocket 3 is coupled with the camshaft. A timing chain 4 drivingly interconnects the crank sprocket 2 and the cam sprocket 3, and circulates in a direction as indicated by arrows B in FIG. 1. A stationary chain guide 5 and a movable chain guide 6 are secured to the cylinder block 10. The stationary chain guide 5 is slidably in contact with the chain 4 at the tension side thereof, whereas the movable chain guide 6 is slidably in contact with the chain 4 at the loose side thereof. A chain tensioner 7 is disposed so as to press the movable chain guide 6 to the timing chain 4.

Referring to FIG. 2, the cylinder head 11 is formed with two camshaft bearings 54 and 55, a flange 56, and a chain case 12. A cam cover 59 is attached to the cylinder head 11 through the flange 56. A chain chamber 57 is defined by the cam cover 59 and a front wall 58 of the cylinder head 11. The chain tensioner 7 is secured to the chain case 12.

As best seen in FIGS. 2 and 3, the chain tensioner 7 includes a body 21 shaped like a cylinder, and a plunger 22 which is slidably received in the body 21. The body 21 received in a bore 13 which is formed with a side wall 12A of the chain case 12. An end portion 22A of the plunger 22 is engaged with the movable chain guide 6.

As best seen in FIGS. 4 and 5, the body 21 includes a generally cylindrical portion 23, and the plunder 22 is slidably received therein. A damping chamber 27 is defined by the cylindrical portion 23 and the plunder 22, whereas an oil reservoir 26 is defined by the bore 13 of the chain case 12 and the body 21.

As best seen in FIGS. 2 and 3, the body 21 has an outer peripheral surface 24 which is opposite to the bore 13 of the chain case 12 at a predetermined interval 30, and two lateral recesses 25 which bring a predetermined volume to the oil reservoir 26. The outer peripheral surface 24 is formed, at one end thereof, with a peripheral cutout 34 which allows fluid communication of the right portion of the oil reservoir 26 with the left portion thereof.

The body 21 includes a flange 28 for attachment to the chain case 12. For oil-tightly sealing the oil reservoir 26, a gasket 29 is interposed between the flange 28 and the chain case 12 and a seal member 31 is interposed between the outer peripheral surface 24 and a wall surface of the bore 13. The chain case 12 also includes a flange 17 for supporting the body 21. The body 21 is secured to the chain case 12 by means of two bolts 20.

As best seen in FIGS. 2 and 5, pressure oil is supplied from an oil pump P to the oil reservoir 26 via an oil supply passage 32 which is formed with the cylinder head 11. An opening 32A of the oil supply passage 32 is located in the oil reservoir 26 at the upper portion thereof, which allows oil storage therein below the opening 32A even upon engine standstill.

As best seen in FIGS. 3 and 4, the chain case 12 if formed with an air bleeder 33 which opens opposite to the outer peripheral surface 24 of the body 21 at the upper portion thereof. Air in the oil reservoir 26 is evacuated to the chain chamber 57 through the air bleeder 33.

As best seen in FIG. 4, for defining an oil passage 40 to allow fluid communication of the oil reservoir 26 with the damping chamber 27, the body 21 is formed with two passage bores 35, and 36: one 35 opens to the lower portion to the peripheral cutout 34, and the other 36 fluidly communicates with the bore 35 and the damping chamber 27. For passing oil exclusively from the oil reservoir 26 to the damping chamber 27, a check valve 37 is installed in the passage bore 36. The check valve 37 includes a sleeve 38 press fitted into the passage bore 36, a ball 39 placed at the bottom of the sleeve 38, a return spring 41 biasing the ball 39, and a retainer (43) receiving the return spring 41.

The plunger 22 is formed with a shift bore 42 in which a spring 44 is installed. The spring 44 is supported, at the one end thereof, by the body 21 through the retainer 43, and biases the plunger 22 in such a direction as to protrude from the body 21. The outer peripheral surface 24 of body 21 is formed, at the upper portion thereof, with a top recess 45, and a passage bore 46 which fluidly communicates with the top recess 45 and the cylinder 23. Defined by the passage bore 46 and a screw 47 press fitted thereinto is a flow restrictor 48 which allows fluid communication of the damping chamber 27 with the oil reservoir 26.

The plunger 22 is formed with a plurality of notches 49 at the outer periphery thereof. Pressed by a spring 52 through a pin 60, a rachet 51 is engaged with one of the plurality of notches 49, which prevents the plunger 22 from withdrawing. As best seen in FIGS. 2 and 3, a hook 53 is arranged between the body 21 and the plunger 22 so as to prevent the plunger 22 from protruding. The hook 53 is disengaged by a slight withdrawl of the plunger 22, so that, upon engine mounting, the chain tensioner 7 can be assembled with the timing chain 4 installed, resulting in easy assembly operation of the chain tensioner 7.

Next, the operation of this embodiment will be described.

Discharged from the oil pump P, oil flows into the oil reservoir 26 via the oil supply passage 32. From this, oil passes through the peripheral cutout 34 and the oil passage 40, and flows into the damping chamber 27 through the check valve 37. On the other hand, as to oil evacuated from the damping chamber 27 under the pressure induced by the timing chain 4, it comes to the top recess 45 via the flow restrictor 48. After overflowing the top recess 45, this oil flows into the oil reservoir 26 via the peripheral cutout 34.

During engine operation, the timing chain 4 inclines to vibrate due to periodic change of the tension induced by a variation in engine speed. The plunger 22 repeatedly protrudes and withdraws through the chain guide 6 in response to the vibration of the chain 4. Oil within the oil reservoir 26 is drawn in the damping chamber 27 via the oil passage 40 when the plunger 22 protrudes, whereas the same within the damping chamber 27 is evacuatted to the top recess 45 via the flow restrictor 48 when the plunger 22 withdraws. The vibration of the timing chain 4 is restrained by the flow resistance which is given to oil flow when passing through the flow restrictor 48.

Air bubbles are found in oil which circulates in the engine 1, and also in the same which flows into the oil reservoir 26 via the oil supply passage 32. The air bubbles separate from oil during stay of oil in the oil reservoir 26, and go up to the upper portion of the oil reservoir 26. Passing through narrow clearance defined by the bore 13 and the outer peripheral surface 24 of the body 21, such air is quickly evacuated outside through the air bleeder 33 formed with the chain case 12.

Since the oil reservoir 26 is formed between the chain case 12 and the body 21, and it has an adequate capacity for oil due to the two lateral recesses 25 of the body 21, and the top recess 45 of the upper portion of the body 21, it is possible to increase the duration of stay of oil in the oil reservoir 26 so as to eliminate enough the air bubbles. Thus, the air is prevented from introducing the damping chamber 27, resulting in a continuation of good buffer action.

Further, oil is stored in the oil reservoir 26 even upon engine standstill so that, when the plunger 22 in a withdrawn position is urged to move in a protruded position upon engine start, oil within the oil reservoir 26 is drawn in the damping chamber 27 via the oil passage 40, thus preventing air suction from the outside.

Still further, since the oil reservoir 26 is formed between the chain case 12 and the body 21, a casing is not needed to define the oil reservoir 26, thus restraining the chain tensioner 7 from enlarging in size.

Still further, since the oil reservoir 26 is defined by the two lateral recesses 25 and the top recess 45 of the body 21, which allows an adequate capacity for oil, a diameter of the bore 13 formed with the chain case 12 can be reduced, thus minimizing decrease in a mechanical strength of the chain case 12.

Furthermore, since the chain case 12 to which the body 21 is attached is integrated with the cylinder head 11, a rigidity for supporting the chain tensioner 7 is sufficiently assured.