JP7534988B2 - Chain tensioner - Google Patents

Description

This invention relates to a chain tensioner used to maintain tension in a chain.

Chain transmission devices used in engines of automobiles and the like include, for example, those that transmit the rotation of the crankshaft to the camshaft, those that transmit the rotation of the crankshaft to accessories such as an oil pump, a water pump, or a supercharger, those that transmit the rotation of the crankshaft to a balancer shaft, and those that connect the intake cam and exhaust cam of a twin cam engine. Chain tensioners are used to keep the chain tension of these chain transmission devices within an appropriate range.

One example of a chain tensioner used for such purposes is described in Patent Document 1. The chain tensioner in Patent Document 1 has a cylinder, a plunger inserted into the cylinder so that it can slide axially, a return spring that urges the plunger in the direction that it protrudes from the cylinder, and a hydraulic damper mechanism that generates a damping force by the viscous resistance of the oil when the plunger moves in the direction that it is pushed into the cylinder.

The cylinder has a cylinder body that is inserted into the tensioner mounting hole in the engine cover, and a cylinder flange that is formed integrally with the cylinder body and fixed in surface contact with the outer surface of the engine cover. The cylinder body is a tubular part with one axial end that is a closed end and the other axial end that is an open end, and is inserted into the tensioner mounting hole with the open end facing inside the engine cover.

The engine cover has an oil hole for supplying oil from the engine's oil pump to the chain tensioner. The cylinder of the chain tensioner has an oil supply passage for introducing oil from the oil hole in the engine cover into the inside of the cylinder. The oil supply passage is an oil introduction hole formed to connect the surface of the cylinder to the inside of the cylinder.

In the chain tensioner of Patent Document 1, when the tension in the chain increases while the engine is running, the tension in the chain causes the plunger to move in a direction that pushes it into the cylinder (hereinafter referred to as the "pushing direction"), absorbing the tension in the chain. At this time, the viscous resistance of the oil inside the cylinder generates a damping force, so the plunger moves slowly.

On the other hand, when the tension in the chain decreases while the engine is running, the force of the return spring and the pressure of the oil in the cylinder cause the plunger to move in the direction in which it protrudes from the cylinder (hereafter referred to as the "protruding direction"), absorbing the slack in the chain.

Patent No. 5102238 (Fig. 2)

Generally, when the engine stops, the engine's oil pump also stops, causing the oil level in the oil hole in the engine cover to drop and air to accumulate in the oil hole. Therefore, when the engine is restarted, the air that has accumulated in the oil hole in the engine cover moves through the oil inlet hole into the cylinder and mixes with the oil in the cylinder. If air gets mixed into the oil in the cylinder, when a load is applied to the plunger in the pushing direction, the air in the cylinder is compressed, causing the plunger to move, resulting in an unstable damping force.

Therefore, to prevent air trapped in the oil hole in the engine cover from flowing into the cylinder when the engine is restarted, the chain tensioner in Patent Document 1 is provided with an air bleed passage that branches off from the middle of the oil inlet hole.

In the chain tensioner of Patent Document 1, the oil introduction hole has an oil inlet that opens into the mating surface of the cylinder flange where the engine cover meets, so that it receives oil directly from the oil hole in the engine cover. An air vent hole is provided so that it branches upward from the middle of the oil introduction hole that connects the oil inlet to the inside of the cylinder, and air that has accumulated in the oil introduction hole can be discharged upward through the air vent hole.

However, when the inventors of the present application prototyped and evaluated the chain tensioner of Patent Document 1 in-house, they found that when air that has accumulated in the oil hole of the engine cover moves through the oil inlet hole of the cylinder and into the interior of the cylinder at engine start, although the air can be discharged through the air vent hole that branches upward from the middle of the oil inlet hole, a considerable amount of air still gets mixed into the oil inside the cylinder.

The inventors of this application therefore investigated the causes of air getting mixed into the oil in the cylinder. As a result, they found that when only air flows into the oil inlet hole from the oil hole in the engine cover at engine start, the air can be smoothly discharged through the air vent hole that branches upward from the middle of the oil inlet hole, but when air is dispersed in the form of air bubbles and contained in the oil flowing into the oil inlet hole from the oil hole in the engine cover, the air in the form of bubbles does not flow from the oil inlet hole into the air vent hole, but flows through the oil inlet hole together with the oil and reaches the inside of the cylinder.

The problem that this invention aims to solve is to provide a chain tensioner that can effectively prevent air from entering the cylinder when the engine is started.

In order to solve the above problems, the present invention provides a chain tensioner having the following configuration.
a cylinder having a cylinder body portion having one axial end that is a closed end and the other axial end that is an open end, the cylinder body portion being inserted into a tensioner mounting hole formed in the engine cover with the open end facing into the engine cover, and a cylinder flange portion being integrally formed with the cylinder body portion and being fixed in surface contact with an outer surface of the engine cover;
a plunger inserted into the cylinder body portion so as to be slidable in the axial direction;
a return spring that biases the plunger in a direction protruding from the cylinder body;
an oil supply passage provided in the cylinder so as to introduce oil into the cylinder body from an oil hole opening in the engine cover;
a hydraulic damper mechanism that generates a damping force by viscous resistance of oil when the plunger moves in a direction to be pushed into the cylinder body,
the oil supply passage includes an oil groove formed in a surface of the cylinder opposite the oil hole so as to receive oil from the oil hole, and an oil introduction hole formed in communication with the oil groove and communicating with the interior of the cylinder body so as to introduce the oil in the oil groove into the interior of the cylinder body,
The oil introduction hole is provided so as to have an oil inlet at a position lower than the oil hole,
The chain tensioner is characterized in that the oil groove has a branching portion that branches the oil received from the oil hole into an upward flow path for bleeding air and a downward flow path connected to the oil inlet.

In this way, an oil groove is formed on the surface of the cylinder that receives oil from the oil hole in the engine cover, and the oil groove has a branching section that branches into an upward flow path and a downward flow path for bleeding air, and the oil inlet of the oil introduction hole located below the oil hole is connected to the downward flow path that branches downward from the branching section. Therefore, even if air is contained in the oil received in the oil groove from the oil hole in the form of air bubbles, the buoyancy acting on the air bubbles makes it difficult for the air to reach the oil inlet of the oil introduction hole connected to the downward flow path, and the air can be effectively discharged through the upward flow path for bleeding air. This makes it possible to effectively prevent air from entering the inside of the cylinder when the engine is started.

It is preferable that the downward flow passage be formed to have a flow passage area larger than the cross-sectional area of the oil hole.

In this way, the flow path area of the downward flow path becomes relatively large, so the effect of the buoyancy of the air bubbles on the viscosity of the oil becomes greater. This makes it possible to effectively prevent air bubbles contained in the oil from passing through the downward flow path and reaching the oil inlet of the oil introduction hole.

the oil groove has a pre-branch flow passage that receives oil from the oil hole and flows the oil to the branch section,
It is preferable to adopt a configuration in which the pre-branch flow passage has a flow passage area larger than a cross-sectional area of the oil hole.

In this way, a pre-branch flow path with a relatively large flow area is provided upstream of the branching section, so air bubbles contained in the oil and the oil tend to separate into upper and lower parts before reaching the branching section. Therefore, air bubbles contained in the oil can be efficiently introduced into the upward flow path for air bleeding at the branching section.

It is preferable that the pre-branch flow path is formed only with flow paths that are horizontal or upward relative to the horizontal.

In this way, the direction of movement of the air bubbles due to buoyancy and the direction of the oil flow in the pre-branch flow path are not opposite to each other, so when the oil flows through the pre-branch flow path, the air bubbles contained in the oil and the oil are smoothly separated into upper and lower parts within the pre-branch flow path. Therefore, the air bubbles contained in the oil can be efficiently introduced into the upward flow path for air bleeding at the branching section.

It is preferable that the pre-branch flow passage be formed in a tapered shape in which the flow passage area gradually expands from the position of the oil hole toward the branching portion.

In this way, as the oil flows from the oil hole toward the branching section, the oil flow area gradually expands, gradually slowing the oil flow rate, making it easier for air bubbles contained in the oil to coalesce in the pre-branching flow path. Therefore, air bubbles contained in the oil can be efficiently introduced into the upward flow path for air bleeding at the branching section.

the branch portion is disposed opposite the oil hole so as to receive oil directly from the oil hole,
It is preferable to adopt a configuration in which a buffer chamber having a cross-sectional area along a horizontal direction larger than a flow path area of the downward flow path is formed in the branching portion.

In this way, the buoyancy of the air bubbles has a greater effect on the viscosity of the oil in the buffer chamber formed in the branching section. This makes it easier for the air bubbles contained in the oil and the oil to separate into upper and lower parts at the branching section, and the air bubbles contained in the oil can be efficiently introduced into the upward flow path for bleeding air at the branching section.

The surface of the cylinder can be a mating surface with the inner periphery of the tensioner mounting hole on the outer periphery of the cylinder body. In other words, the oil groove can be formed on the mating surface with the inner periphery of the tensioner mounting hole on the outer periphery of the cylinder body.

The surface of the cylinder can be a mating surface of the cylinder flange portion with the outer surface of the engine cover. That is, the oil groove can be formed on the mating surface of the cylinder flange portion with the outer surface of the engine cover.

The chain tensioner of this invention has an oil groove formed on the surface of the cylinder that receives oil from an oil hole in the engine cover, and the oil groove has a branching section that branches the oil received from the oil hole into an upward flow path for bleeding air and a downward flow path that connects to the oil inlet of the oil introduction hole located below the oil hole. Therefore, even if the oil received in the oil groove from the oil hole contains air in the form of bubbles, the air is likely to separate from the oil at the branching section of the oil groove and is unlikely to reach the oil inlet of the oil introduction hole connected to the downward flow path. This makes it possible to effectively prevent air from entering the inside of the cylinder when the engine is started.

FIG. 1 is a diagram showing a chain transmission device incorporating a chain tensioner according to a first embodiment of the present invention; Enlarged view of the area around the chain tensioner in Figure 1 A cross-sectional view of the chain tensioner of FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. Cross-sectional view taken along line V-V in FIG. FIG. 3 is a diagram showing a modified example of the pre-branch flow path shown in FIG. 2 . FIG. 3 is a diagram showing another modified example of the pre-branch flow path shown in FIG. 2 . FIG. 3 is a diagram showing yet another modified example of the pre-branch flow path shown in FIG. 2 . FIG. 4 is a cross-sectional view showing a chain tensioner according to a second embodiment of the present invention. FIG. 13 is a diagram showing a chain transmission device incorporating a chain tensioner according to a third embodiment of the present invention. FIG. 11 is an enlarged cross-sectional view of the vicinity of the chain tensioner in FIG. 12 is a cross-sectional view taken along line XII-XII of FIG. 13 is a cross-sectional view taken along line XIII-XIII of FIG. FIG. 13 is a perspective view of the cylinder flange portion shown in FIG. 12 . FIG. 11 is a cross-sectional view showing a chain tensioner according to a fourth embodiment of the present invention.

Figure 1 shows a chain transmission device incorporating a chain tensioner 1 according to a first embodiment of the present invention. In this chain transmission device, a sprocket 3 fixed to an engine crankshaft 2 and a sprocket 5 fixed to a camshaft 4 are connected via a chain 6, and the chain 6 transmits the rotation of the crankshaft 2 to the camshaft 4, and the rotation of the camshaft 4 opens and closes the valves (not shown) in the combustion chamber.

When the engine is running, the crankshaft 2 rotates in a constant direction (clockwise in the figure), and the part of the chain 6 that is pulled into the sprocket 3 as the crankshaft 2 rotates (right side of the figure) is the tight side, and the part that is sent out from the sprocket 3 (left side of the figure) is the slack side. The slack side of the chain 6 is in contact with a chain guide 8 that is supported so that it can swing around a fulcrum shaft 7. The chain tensioner 1 presses against the chain 6 via the chain guide 8.

As shown in FIG. 2, the chain tensioner 1 has a cylinder 10 that is fixed to the engine cover 9. The cylinder 10 has a cylinder body 10A that is inserted into a tensioner mounting hole 11 in the engine cover 9, and a cylinder flange 10B that is fixed in surface contact with the outer surface 12 of the engine cover 9. The cylinder body 10A and the cylinder flange 10B are formed seamlessly as one piece from an aluminum alloy.

The engine cover 9 is a wall that forms the chain storage chamber 13 in which the chain 6 (see FIG. 1) is stored. The tensioner mounting hole 11 is formed penetrating from the outer surface 12 (the surface opposite the chain storage chamber 13) of the engine cover 9 to the inner surface (the surface on the side of the chain storage chamber 13).

The cylinder flange portion 10B is fixed to the engine cover 9 with bolts 14. The cylinder flange portion 10B is formed with a mating surface 15 that comes into surface contact with the outer surface 12 of the engine cover 9. The gap between the mating surface 15 and the outer surface 12 of the engine cover 9 is sealed by tightening the bolts 14. The outer periphery of the cylinder body portion 10A is formed with a cylindrical mating surface 16 that fits into the inner periphery of the tensioner mounting hole 11.

As shown in FIG. 3, the chain tensioner 1 has a plunger 17 inserted into the cylinder body 10A so as to be axially slidable, a return spring 18 that biases the plunger 17 in a direction that causes it to protrude from the cylinder body 10A, and a hydraulic damper mechanism 19 that generates a damping force by the viscous resistance of oil when the plunger 17 moves in a direction that causes it to be pushed into the cylinder body 10A.

The cylinder body 10A is formed in a cylindrical shape with one axial end being a closed end and the other axial end being an open end. The cylinder body 10A is inserted into the tensioner mounting hole 11 with the open end facing inside the engine cover 9. The cylinder flange 10B is formed on the outer periphery of the end of the cylinder body 10A on the closed end side.

The end of the plunger 17 protruding from the cylinder body 10A presses against the chain guide 8. The cylinder 10 is mounted in a position in which the plunger 17 protrudes from the cylinder body 10A in a direction that is inclined downward from the horizontal. The plunger 17 may also be mounted in a position in which the plunger 17 protrudes from the cylinder body 10A in a horizontal direction.

The plunger 17 is formed in a cylindrical shape with an open end that is inserted into the cylinder body 10A and a closed end that protrudes from the cylinder body 10A. The plunger 17 is made of an iron-based material (e.g., steel such as SCM (chrome molybdenum steel) or SCr (chrome steel)).

The inner sleeve 20 is inserted into the plunger 17 so that one axial end is inserted into the plunger 17 and the other axial end protrudes from the plunger 17. The end of the inner sleeve 20 protruding from the plunger 17 is supported by the closed end of the cylinder body 10A. A check valve 21 is provided at the end of the inner sleeve 20 inserted into the plunger 17.

The check valve 21 divides the internal area of the inner sleeve 20 and the plunger 17 into a reservoir chamber 22 on the inner sleeve 20 side and a pressure chamber 23 on the plunger 17 side. The volume of the reservoir chamber 22 does not change even when the plunger 17 moves axially and is constant. On the other hand, the volume of the pressure chamber 23 expands when the plunger 17 moves axially in a direction protruding from the cylinder body 10A, and contracts when the plunger 17 moves axially in a direction being pushed into the cylinder body 10A. The check valve 21 restricts the flow of oil from the pressure chamber 23 side to the reservoir chamber 22 side, and allows oil to flow only from the reservoir chamber 22 side to the pressure chamber 23 side.

A return spring 18 is installed in the pressure chamber 23. The return spring 18 is a compression coil spring made of metal wire wound in a spiral shape. One end of the return spring 18 is supported by the check valve 21, and the other end presses the plunger 17 in the axial direction, and this pressing force urges the plunger 17 in the direction of protruding from the cylinder body 10A.

A leak gap 24 is formed between the outer periphery of the inner sleeve 20 and the inner periphery of the plunger 17, which allows oil to leak from the pressure chamber 23 when the volume of the pressure chamber 23 decreases. The leak gap 24 is a minute cylindrical gap whose radial width is set in the range of 0.010 to 0.050 mm.

A cylindrical guide gap 25 is formed between the inner circumference of the cylinder body 10A and the outer circumference of the plunger 17. The radial width of the guide gap 25 is set to be larger than the radial width of the leak gap 24, and can be set in the range of 0.015 to 0.065 mm, for example.

Here, the reservoir chamber 22, the pressure chamber 23, the check valve 21, and the leak gap 24 constitute the hydraulic damper mechanism 19. That is, when the plunger 17 moves in a direction protruding from the cylinder body 10A, the check valve 21 opens, introducing hydraulic oil from the reservoir chamber 22 into the pressure chamber 23, and when the plunger 17 moves in a direction pushing into the cylinder body 10A, the check valve 21 closes, causing oil to flow out of the pressure chamber 23 through the leak gap 24, and the viscous resistance of the oil generates a damping force.

The part of the inner sleeve 20 that protrudes from the plunger 17 is provided with an oil passage 27 that connects the cylindrical space 26 to the reservoir chamber 22. The cylindrical space 26 is a cylindrical region that is radially sandwiched between the inner circumference of the cylinder body 10A and the outer circumference of the inner sleeve 20 on the side closer to the closed end of the cylinder body 10A than the insertion end of the plunger 17 into the cylinder body 10A. The oil passage 27 is a through hole that is formed by penetrating the inner sleeve 20 in the radial direction.

As shown in Figures 2 and 5, the engine cover 9 is formed with an oil hole 30 for supplying oil from the engine's oil pump (not shown) to the chain tensioner 1. The oil hole 30 is a circular hole with a circular cross-sectional shape. The oil hole 30 opens to the inner circumference of the tensioner mounting hole 11 in the engine cover 9.

The cylinder 10 is provided with an oil supply passage 31 that introduces oil supplied from the oil hole 30 into the interior of the cylinder body 10A. The oil supply passage 31 has an oil groove 32 formed on the surface of the cylinder 10 (here, the cylindrical fitting surface 16 on the outer periphery of the cylinder body 10A) and an oil introduction hole 33 (see FIG. 4) formed in communication with the oil groove 32 and the interior of the cylinder body 10A so as to introduce the oil in the oil groove 32 into the interior of the cylinder body 10A.

As shown in FIG. 2, the oil groove 32 has a pre-branch flow path 34, a branching portion 35, an upward flow path 36, and a downward flow path 37. The pre-branch flow path 34 is a flow path that receives oil from the oil hole 30 and flows the oil to the branching portion 35. The upstream end of the pre-branch flow path 34 is disposed radially opposite the opening of the oil hole 30 on the inner circumference of the tensioner mounting hole 11 so as to receive oil directly from the oil hole 30, and the downstream end of the pre-branch flow path 34 is connected to the branching portion 35 so as to allow the oil flowing from the oil hole 30 to flow into the branching portion 35.

The pre-branch flow passage 34 is formed only with a flow passage that faces upward relative to the horizontal. In the figure, the pre-branch flow passage 34 is shown as a flow passage that extends upward to the upper right relative to the horizontal and then upward to the left relative to the horizontal. The pre-branch flow passage 34 may further include a horizontal flow passage. The pre-branch flow passage 34 is a rectangular groove with a square cross-sectional shape. The pre-branch flow passage 34 has a flow passage area (cross-sectional area of the flow passage along a cross section perpendicular to the oil flow direction) that is larger than the cross-sectional area of the oil hole 30.

The branching section 35 is a section where the pre-branching flow path 34, the upward flow path 36, and the downward flow path 37 are connected so that the oil received from the oil hole 30 in the pre-branching flow path 34 branches off and flows into the upward flow path 36 and the downward flow path 37. The upward flow path 36 is an air bleeding flow path that discharges air upward from the branching section 35, and is connected to the chain storage chamber 13 inside the engine cover 9 via an orifice passage 38 and an air bleeding passage 39.

The upward flow passage 36 is formed by extending upward from the branching portion 35 around the outer periphery of the cylinder body portion 10A. The upward flow passage 36 is a rectangular groove with a square cross-sectional shape. The upward flow passage 36 is formed to have a flow passage area larger than the cross-sectional area of the oil hole 30. The orifice passage 38 is a minute annular groove formed on the outer periphery of the cylinder body portion 10A. The air bleed passage 39 is a gap formed between the inner periphery of the tensioner mounting hole 11 and the outer periphery of the cylinder body portion 10A.

As shown in FIG. 4, the downward flow passage 37 is formed by extending downward from the branching portion 35 around the outer periphery of the cylinder body portion 10A. The downward flow passage 37 is a rectangular groove having a rectangular cross-sectional shape. The downward flow passage 37 is formed to have a flow passage area larger than the cross-sectional area of the oil hole 30. The downward flow passage 37 is connected to the oil inlet 33a of the oil introduction hole 33. The oil introduction hole 33 is a hole formed by penetrating the lower peripheral wall portion of the cylinder body portion 10A in the radial direction. The oil inlet 33a is an opening portion of the oil introduction hole 33 on the outer periphery side of the cylinder body portion 10A. The oil inlet 33a is located below the opening position of the oil hole 30 (see FIG. 5).

Next, we will explain an example of how this chain tensioner 1 works.

When the tension of the chain 6 shown in FIG. 1 increases during engine operation, the tension of the chain 6 causes the plunger 17 to move in a direction that pushes it into the cylinder body 10A, absorbing the tension of the chain 6. At this time, the pressure of the pressure chamber 23 shown in FIG. 3 becomes higher than the pressure of the reservoir chamber 22, so the check valve 21 is closed. In addition, the volume of the pressure chamber 23 decreases in response to the movement of the plunger 17, so oil leaks from the pressure chamber 23 through the leak gap 24 by the amount of the decreased volume. At this time, a damping force is generated by the viscous resistance of the oil flowing through the leak gap 24, and this damping force prevents the chain 6 from flapping. Most of the oil that leaks from the pressure chamber 23 through the leak gap 24 to the cylindrical space 26 returns to the reservoir chamber 22 through the oil passage 27. In addition, a portion of the oil that leaks from the pressure chamber 23 through the leak gap 24 to the cylindrical space 26 lubricates the guide gap 25.

On the other hand, when the tension of the chain 6 shown in FIG. 1 decreases during engine operation, the force of the return spring 18 shown in FIG. 3 and the oil pressure of the pressure chamber 23 move the plunger 17 in the protruding direction, absorbing the slack in the chain 6. At this time, the volume of the pressure chamber 23 expands in response to the movement of the plunger 17, so that the pressure of the pressure chamber 23 becomes lower than the pressure of the reservoir chamber 22, and the check valve 21 opens. Then, oil flows from the reservoir chamber 22 through the check valve 21 into the pressure chamber 23, and the plunger 17 moves quickly. At this time, as shown by the dashed arrows in FIG. 2 and FIG. 4, the oil supplied from the oil hole 30 is introduced into the inside of the cylinder body 10A through the pre-branch flow path 34, the branch portion 35, the downward flow path 37, and the oil introduction hole 33 of the oil groove 32 in that order.

When the engine stops, the engine oil pump also stops, so the oil level in the oil hole 30 of the engine cover 9 drops, and air accumulates in the oil hole 30. When the engine is then restarted, first, only air flows from the oil hole 30 of the engine cover 9 into the oil groove 32. At this time, the air passes through the pre-branch flow path 34 of the oil groove 32, the branching section 35, the upward flow path 36, the orifice passage 38, and the air bleed passage 39 in order, and is discharged to the chain storage chamber 13. Next, oil begins to flow from the oil hole 30 of the engine cover 9 into the oil groove 32. At this time, air may be dispersed and contained in the oil in the form of air bubbles, but the air bubbles and oil contained in the oil flow separately up and down in the pre-branch flow path 34 due to the buoyancy acting on the air bubbles, and at the branching section 35, the air bubbles flow into the upward flow path 36 and the oil flows into the downward flow path 37. Air bubbles that flow into the upward flow path 36 are discharged into the chain storage chamber 13 via the orifice passage 38 and the air vent passage 39 in that order. Oil that flows into the downward flow path 37 flows into the inside of the cylinder body 10A through the oil introduction hole 33.

As shown in FIG. 2, this chain tensioner 1 has an oil groove 32 formed on the surface of the cylinder 10 to receive oil from the oil hole 30 of the engine cover 9, and the oil groove 32 has a branching portion 35 that branches into an upward flow path 36 and a downward flow path 37 for bleeding air. The oil inlet 33a (see FIG. 4) of the oil introduction hole 33 located below the oil hole 30 is connected to the downward flow path 37 that branches downward from the branching portion 35. Therefore, even if air is contained in the oil received in the oil groove 32 from the oil hole 30 in the form of air bubbles, the buoyancy acting on the air bubbles makes it difficult for the air to reach the oil inlet 33a of the oil introduction hole 33 connected to the downward flow path 37, and the air can be effectively discharged through the upward flow path 36 for bleeding air. Therefore, it is possible to effectively prevent air from entering the inside of the cylinder 10 when the engine is started.

In addition, in this chain tensioner 1, the downward flow passage 37 shown in FIG. 2 has a flow passage area larger than the cross-sectional area of the oil hole 30, and since the flow passage area of the downward flow passage 37 is relatively large, the buoyancy of the air bubbles has a large effect on the viscosity of the oil in the downward flow passage 37. Therefore, it is possible to effectively prevent air bubbles contained in the oil from passing through the downward flow passage 37 and reaching the oil inlet 33a of the oil introduction hole 33.

In addition, this chain tensioner 1 has a pre-branch flow passage 34 with a flow passage area larger than the cross-sectional area of the oil hole 30, which is provided upstream of the branching section 35, so that air bubbles contained in the oil and the oil tend to separate into upper and lower parts before reaching the branching section 35. This makes it possible to efficiently introduce air bubbles contained in the oil into the upward flow passage 36 for bleeding air at the branching section 35.

In addition, as shown in FIG. 2, the pre-branch flow passage 34 of this chain tensioner 1 is formed only with horizontal or upward flow passages relative to the horizontal, so the movement direction of air bubbles due to buoyancy is never reversed to the direction of oil flow in the pre-branch flow passage 34. Therefore, when the oil flows through the pre-branch flow passage 34, the air bubbles contained in the oil and the oil are smoothly separated into upper and lower parts within the pre-branch flow passage 34. As a result, it is possible to efficiently introduce the air bubbles contained in the oil into the upward flow passage 36 for bleeding air at the branch section 35.

As shown in FIG. 6, the pre-branch flow passage 34 can be formed to have a portion that extends at an upward incline toward the branch portion 35 with respect to the axial direction of the cylinder body 10A. In this way, when the cylinder 10 is attached in a position in which the plunger 17 (see FIG. 2) protrudes from the cylinder body 10A in a horizontal direction or in a direction inclined downward from the horizontal, the pre-branch flow passage 34 can be reliably inclined upward from the horizontal. In addition, the inclination of the pre-branch flow passage 34 brings the branch portion 35 to a relatively high position, so the length of the downward flow passage 37 is increased. Therefore, a relatively large amount of oil can be stored in the downward flow passage 37 when the engine is stopped, and the oil can be used to quickly exert a damping force when the engine is started.

Also, as shown in FIG. 6, the pre-branch flow path 34 can be formed in a tapered shape in which the flow path area gradually expands from the position of the oil hole 30 toward the branching section 35. In this way, when the oil flows from the position of the oil hole 30 toward the branching section 35, the flow path area of the oil gradually expands, gradually slowing the flow rate of the oil, so that air bubbles contained in the oil tend to coalesce in the pre-branch flow path 34. Therefore, air bubbles contained in the oil can be efficiently introduced into the upward flow path 36 for air bleeding at the branching section 35.

As shown in FIG. 7, the pre-branch flow path 34 may be formed so that its entire length extends at an upward incline toward the branch portion 35 with respect to the axial direction of the cylinder body 10A.

In the above embodiment, the pre-branch flow path 34 is formed on the side of the open end of the cylinder body 10A (on the right side in the figure) relative to the upward flow path 36 and the downward flow path 37. However, as shown in FIG. 8, the pre-branch flow path 34 may be formed on the side of the closed end of the cylinder body 10A (on the left side in the figure) relative to the upward flow path 36 and the downward flow path 37, and the pre-branch flow path 34 may be formed to extend at an upward incline toward the branch portion 35 relative to the axial direction of the cylinder body 10A. In this way, even when the cylinder 10 is attached in a position in which the direction in which the plunger 17 (see FIG. 2) protrudes from the cylinder body 10A is inclined upward from the horizontal, the pre-branch flow path 34 can be reliably inclined upward from the horizontal.

Figure 9 shows the chain tensioner 1 of the second embodiment. The second embodiment differs from the first embodiment only in the internal structure of the cylinder body 10A, and the other configurations (including the configuration of the oil supply passage 31) are the same. Therefore, parts corresponding to the first embodiment are given the same reference numerals and descriptions are omitted.

A pressure chamber 23 surrounded by the cylinder body 10A and the plunger 17 is formed within the cylinder body 10A. A reservoir chamber 22 is formed at the closed end of the cylinder. A check valve 21 is provided between the pressure chamber 23 and the reservoir chamber 22.

A leak gap 24 is formed between the outer periphery of the plunger 17 and the inner periphery of the cylinder body 10A, allowing oil to leak from the pressure chamber 23 when the volume of the pressure chamber 23 decreases.

At the end of the plunger 17 protruding from the cylinder body 10A, a relief passage 40 is formed that connects the pressure chamber 23 to the chain storage chamber 13. The relief passage 40 is provided with a relief valve 41 that opens when the pressure in the pressure chamber 23 exceeds a preset pressure.

The oil inlet hole 33 is a hole formed by penetrating the lower peripheral wall portion of the cylinder body portion 10A in the radial direction, and connects the oil groove 32 and the reservoir chamber 22.

The reservoir chamber 22, the pressure chamber 23, the check valve 21, and the leak gap 24 constitute the hydraulic damper mechanism 19. That is, when the plunger 17 moves in a direction protruding from the cylinder body 10A, the check valve 21 opens, introducing hydraulic oil from the reservoir chamber 22 into the pressure chamber 23, and when the plunger 17 moves in a direction pushing into the cylinder body 10A, the check valve 21 closes, allowing oil to flow out of the pressure chamber 23 through the leak gap 24, and the viscous resistance of the oil generates a damping force.

An assist spring 42 is installed between the insertion end of the plunger 17 into the cylinder body 10A and the closed end of the cylinder body 10A. The assist spring 42 assists the force of the return spring 18 pressing the plunger 17, thereby improving the ability of the chain guide 8 to follow the chain 6.

The chain tensioner 1 of this second embodiment has the same effect as the first embodiment.

Figure 10 shows a chain transmission device incorporating a chain tensioner 1 according to a third embodiment of the present invention. The third embodiment differs from the first embodiment only in the opening position of the oil hole 30 in the engine cover 9, the mounting attitude of the cylinder 10 relative to the engine cover 9, and the configuration of the oil groove 32 and oil introduction hole 33 formed in the cylinder 10; the rest of the configuration is the same. Therefore, parts corresponding to those in the first embodiment are given the same reference numerals and will not be described.

The cylinder 10 is attached to the engine cover 9 in such a position that the plunger 17 protrudes from the cylinder body 10A in the horizontal direction. The plunger 17 may also be attached in such a position that the protrusion direction of the plunger 17 from the cylinder body 10A is inclined downward from the horizontal.

As shown in FIG. 13, the engine cover 9 is formed with an oil hole 30 for supplying oil from the engine's oil pump (not shown) to the chain tensioner 1. The oil hole 30 is a round hole with a circular cross-sectional shape. The oil hole 30 opens to the outer surface 12 of the engine cover 9.

The cylinder 10 is provided with an oil supply passage 31 that introduces oil supplied from the oil hole 30 into the interior of the cylinder body 10A. The oil supply passage 31 has an oil groove 32 formed on the surface of the cylinder 10 (here, the mating surface 15 of the cylinder flange 10B with the outer surface 12 of the engine cover 9) and an oil introduction hole 33 (see FIG. 11) formed in communication with the oil groove 32 and the interior of the cylinder body 10A so as to introduce the oil in the oil groove 32 into the interior of the cylinder body 10A.

As shown in FIG. 12, the oil groove 32 has a branching portion 35, an upward flow path 36, and a downward flow path 37. The branching portion 35 is arranged axially opposite the opening of the oil hole 30 on the outer surface 12 of the engine cover 9 (see FIG. 13) so as to receive oil directly from the oil hole 30. A buffer chamber 43 is formed in the branching portion 35. The buffer chamber 43 is a recess formed by recessing in a columnar shape from the mating surface 15 of the cylinder flange portion 10B with the outer surface 12 of the engine cover 9 (see FIG. 13). As shown in FIG. 12, the vertical height dimension and horizontal width dimension of the buffer chamber 43 are both larger than the inner diameter of the oil hole 30. Also, as shown in FIG. 13, the cross-sectional area of the buffer chamber 43 along the horizontal direction is larger than the flow path area of the downward flow path 37.

As shown in FIG. 12, the upward flow passage 36 is formed by extending in an arc shape upward from the branching portion 35 along the outer periphery of the cylinder body portion 10A. The upward flow passage 36 is a rectangular groove having a rectangular cross-sectional shape. The upward flow passage 36 is formed to have a flow passage area larger than the cross-sectional area of the oil hole 30.

As shown in FIG. 11, the upward flow path 36 is connected to an air bleed passage 39 above the cylinder body 10A, and communicates with the chain storage chamber 13 inside the engine cover 9 via the air bleed passage 39. The air bleed passage 39 is a small gap formed between the inner circumference of the tensioner mounting hole 11 and the outer circumference of the cylinder body 10A. As shown in FIG. 14, this air bleed passage 39 can be formed by providing a D-cut portion 44 (a portion with a shape obtained by removing the outer circumference of the cylinder body 10A along a plane parallel to the axis of the cylinder body 10A) that extends axially along the upper outer circumference of the cylinder body 10A.

As shown in FIG. 12, the downward flow passage 37 is formed by extending in an arc shape downward from the branching portion 35 along the outer periphery of the cylinder body portion 10A. The downward flow passage 37 is a rectangular groove having a rectangular cross-sectional shape. The downward flow passage 37 is formed to have a flow passage area larger than the cross-sectional area of the oil hole 30. The downward flow passage 37 is connected to the oil inlet 33a of the oil introduction hole 33.

As shown in FIG. 11, the oil introduction hole 33 is composed of a vertical hole portion 45 formed by penetrating the lower part of the cylinder flange portion 10B in the radial direction, and a horizontal hole portion 46 formed by extending in the axial direction from the mating surface 15 of the cylinder flange portion 10B to the vertical hole portion 45. The end of the vertical hole portion 45 on the outer periphery side of the cylinder flange portion 10B is blocked by a plug member 47. The plug member 47 is a male thread member in the figure. The oil inlet 33a of the oil introduction hole 33 is the opening portion on the mating surface 15 side of the horizontal hole portion 46 of the oil introduction hole 33. As shown in FIG. 12, the oil inlet 33a is located below the opening position of the oil hole 30.

An example of the operation of this chain tensioner 1 will be described. As in the first embodiment, when the engine stops, the engine oil pump also stops, so the oil level in the oil hole 30 of the engine cover 9 drops, and air accumulates in the oil hole 30. When the engine is then restarted, first, only air flows from the oil hole 30 of the engine cover 9 into the oil groove 32. At this time, the air passes through the branching portion 35 of the oil groove 32, the upward flow path 36, and the air vent passage 39 in order, and is discharged into the chain storage chamber 13. Next, oil begins to flow from the oil hole 30 of the engine cover 9 into the oil groove 32. At this time, air may be dispersed and contained in the oil in the form of air bubbles, but the air bubbles and oil contained in the oil are separated into upper and lower parts at the branching portion 35 due to the buoyancy acting on the air bubbles, and the air bubbles flow into the upward flow path 36 and the oil flows into the downward flow path 37. The air bubbles that flow into the upward flow path 36 are discharged into the chain storage chamber 13 through the air vent passage 39. The oil that flows into the downward flow path 37 flows through the oil inlet hole 33 into the inside of the cylinder body 10A.

As shown in FIG. 12, this chain tensioner 1 has an oil groove 32 formed on the surface of the cylinder 10 to receive oil from the oil hole 30, and the oil groove 32 has a branching portion 35 that branches into an upward flow path 36 and a downward flow path 37 for bleeding air. The oil inlet 33a of the oil introduction hole 33 located below the oil hole 30 is connected to the downward flow path 37 that branches downward from the branching portion 35. Therefore, even if air is contained in the oil received in the oil groove 32 from the oil hole 30 in the form of air bubbles, the buoyancy acting on the air bubbles makes it difficult for the air to reach the oil inlet 33a of the oil introduction hole 33 connected to the downward flow path 37, and the air can be effectively discharged through the upward flow path 36 for bleeding air. Therefore, it is possible to effectively prevent air from entering the inside of the cylinder 10 when the engine is started.

In addition, in this chain tensioner 1, the downward flow passage 37 shown in FIG. 12 has a flow passage area larger than the cross-sectional area of the oil hole 30, and since the flow passage area of the downward flow passage 37 is relatively large, the buoyancy of the air bubbles has a large effect on the viscosity of the oil in the downward flow passage 37. Therefore, it is possible to effectively prevent air bubbles contained in the oil from passing through the downward flow passage 37 and reaching the oil inlet 33a of the oil introduction hole 33.

In addition, as shown in FIG. 13, in this chain tensioner 1, the buffer chamber 43 formed in the branching section 35 has a cross-sectional area larger than the flow passage area of the downward flow passage 37, so that the buoyancy of the air bubbles has a large effect on the viscosity of the oil in the buffer chamber 43. Therefore, the air bubbles contained in the oil and the oil are easily separated into upper and lower parts at the branching section 35, and the air bubbles contained in the oil can be efficiently introduced into the upward flow passage 36 for bleeding air at the branching section 35.

Figure 15 shows the chain tensioner 1 of the fourth embodiment. The fourth embodiment differs from the third embodiment only in the internal structure of the cylinder body 10A, and the rest of the configuration is the same. The internal structure of the cylinder body 10A is also the same as in the second embodiment. Therefore, parts corresponding to the second and third embodiments are given the same reference numerals and descriptions are omitted.

In each of the above embodiments, an example has been described in which the chain tensioner 1 is incorporated into a chain transmission device that transmits the rotation of the crankshaft 2 to the camshaft 4, but the chain tensioner 1 can also be incorporated into a chain transmission device that transmits the rotation of the crankshaft to an auxiliary device such as an oil pump, a water pump, or a supercharger, a chain transmission device that transmits the rotation of the crankshaft to a balancer shaft, or a chain transmission device that connects the intake cam and exhaust cam of a twin cam engine.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

REFERENCE SIGNS LIST 1 Chain tensioner 9 Engine cover 10 Cylinder 10A Cylinder body 10B Cylinder flange 11 Tensioner mounting hole 12 Outer surface 15 Mating surface 16 Fitting surface 17 Plunger 18 Return spring 19 Hydraulic damper mechanism 30 Oil hole 31 Oil supply passage 32 Oil groove 33 Oil introduction hole 33a Oil inlet 34 Pre-branch flow path 35 Branch portion 36 Upward flow path 37 Downward flow path 43 Buffer chamber

Claims (8)

a cylinder (10) having a cylinder body portion (10A) having one axial end which is a closed end and the other axial end which is an open end, the cylinder body portion (10A) being inserted into a tensioner mounting hole (11) formed in the engine cover (9) with the open end facing into the engine cover (9), and a cylinder flange portion (10B) which is integrally formed with the cylinder body portion (10A) and which is fixed in surface contact with an outer surface (12) of the engine cover (9);
a plunger (17) inserted into the cylinder body (10A) so as to be slidable in the axial direction;
a return spring (18) that biases the plunger (17) in a direction that causes the plunger to protrude from the cylinder body portion (10A);
an oil supply passage (31) provided in the cylinder (10) so as to introduce oil into the inside of the cylinder body (10A) from an oil hole (30) opening in the engine cover (9);
a hydraulic damper mechanism (19) that generates a damping force by viscous resistance of oil when the plunger (17) moves in a direction to be pushed into the cylinder body portion (10A),
the oil supply passage (31) has an oil groove (32) formed in the surface of the cylinder (10) opposite the oil hole (30) so as to receive oil from the oil hole (30), and an oil introduction hole (33) formed in communication from the oil groove (32) to the inside of the cylinder body portion (10A) so as to introduce the oil in the oil groove (32) into the inside of the cylinder body portion (10A),
The oil introduction hole (33) is provided so as to have an oil inlet (33a) at a position lower than the oil hole (30),
The oil groove (32) has a branching portion (35) that branches the oil received from the oil hole (30) into an upward flow path (36) for bleeding air and a downward flow path (37) connected to the oil inlet (33 a). The chain tensioner according to claim 1, wherein the downward flow passage (37) is formed to have a flow passage area larger than the cross-sectional area of the oil hole (30). The oil groove (32) has a pre-branch flow path (34) that receives oil from the oil hole (30) and flows it to the branch portion (35),
3. The chain tensioner according to claim 1, wherein the pre-branch flow passage (34) has a flow passage area larger than a cross-sectional area of the oil hole (30). The chain tensioner according to claim 3, wherein the pre-branch flow passage (34) is formed only with flow passages that are horizontal or upward relative to the horizontal. The chain tensioner according to claim 3 or 4, wherein the pre-branch flow passage (34) is formed in a tapered shape in which the flow passage area gradually expands from the position of the oil hole (30) toward the branch portion (35). The branch portion (35) is disposed opposite the oil hole (30) so as to receive oil directly from the oil hole (30);
3. The chain tensioner according to claim 1, wherein a buffer chamber (43) is formed in the branch portion (35) and the cross-sectional area along the horizontal direction is larger than the flow path area of the downward flow path (37). A chain tensioner according to any one of claims 1 to 6, wherein the surface of the cylinder (10) is a mating surface (16) with the inner periphery of the tensioner mounting hole (11) on the outer periphery of the cylinder body (10A). A chain tensioner according to any one of claims 1 to 6, wherein the surface of the cylinder (10) is a mating surface (15) of the cylinder flange portion (10B) with the outer surface (12) of the engine cover (9).

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