Hydraulic chain tensioner

Abstract

To improve discharge performance for air mixed into a pressure chamber, in a hydraulic chain tensioner having a coil spring for pressing an insertion end against a cylinder of a plunger.SOLUTION: In a hydraulic chain tensioner 1 having a coil spring 36 arranged coaxially in a cylinder 9 so as to press an insertion end of a plunger 10 into the cylinder 9, and used in a posture in which a direction in which the plunger 10 protrudes from the cylinder 9 is upward with respect to horizontal, an air accommodating recess part 37 is formed in at least a portion of an inner periphery of the cylinder 9 facing the upper side of the coil spring 36 so that the air accommodating recess part is recessed radially outward relative to a radial position of an inner peripheral cylindrical surface 27 and adjacent to a leak gap 26 in an axial direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This invention relates to a hydraulic chain tensioner that is primarily used to maintain tension on a chain that drives a cam in an automobile engine. [Background technology]

[0002] Chain transmission devices used in engines of automobiles, motorcycles, etc. include those that transmit crankshaft rotation to camshafts, those that transmit crankshaft rotation to accessories such as oil pumps, water pumps, and superchargers, those that transmit crankshaft rotation to balancer shafts, and those that connect the intake cam and exhaust cam of a twin-cam engine. Hydraulic chain tensioners are used to maintain the chain tension of these chain transmission devices within an appropriate range.

[0003] A known example of a hydraulic chain tensioner used for such purposes is that disclosed in Patent Document 1. The hydraulic chain tensioner in Patent Document 1 includes a cylindrical cylinder with a bottom, a plunger supported so as to be axially slidable on an inner cylindrical surface formed on the inner periphery of the cylinder, a pressure chamber surrounded by the cylinder and plunger, an oil supply passage that supplies hydraulic oil to the pressure chamber, a check valve provided at the end of the oil supply passage on the pressure chamber side, and a leak gap formed between the inner cylindrical surface of the cylinder and the outer periphery of the plunger.

[0004] In the hydraulic chain tensioner of Patent Document 1, when chain tension increases while the engine is running, the chain tension causes the plunger to move in a direction pushing into the cylinder, absorbing the chain tension. At this time, a damping force is generated by the viscous resistance of the hydraulic oil flowing out of the pressure chamber through the leak gap, causing the plunger to move slowly. On the other hand, when chain tension decreases while the engine is running, the pressure of the hydraulic oil in the pressure chamber causes the plunger to move in a direction protruding from the cylinder, absorbing the chain slack. At this time, the check valve opens, allowing hydraulic oil to flow into the pressure chamber from the oil supply passage, causing the plunger to move quickly. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3635198 Summary of the Invention [Problem to be solved by the invention]

[0006] In the hydraulic chain tensioner described above, air can become mixed into the hydraulic oil in the pressure chamber when a sudden drop in pressure in the pressure chamber causes air to separate from the hydraulic oil in the pressure chamber, or when hydraulic oil containing air is supplied from the oil pump.If air becomes mixed into the hydraulic oil in the pressure chamber, when the tension on the chain increases, the plunger moves due to a change in the volume of air in the pressure chamber, which causes a problem of a decrease in the damping force of the hydraulic chain tensioner (so-called air entrapment).

[0007] 14, in order to discharge air from the pressure chamber 50 when air gets mixed in with the hydraulic oil inside the pressure chamber 50, hydraulic chain tensioners that are used in an orientation in which the direction in which the plunger 51 protrudes from the cylinder 52 is upward relative to the horizontal are often provided with an air vent passage 53 at the end of the plunger 51 protruding from the cylinder 52. When this air vent passage 53 is provided, air that has accumulated inside the pressure chamber 50 inside the plunger 51 is discharged to the outside through the air vent passage 53 provided at the end of the plunger 51 protruding from the cylinder 52. Furthermore, air that has accumulated along the inner periphery of the cylinder 52 in the pressure chamber 50 is discharged to the outside through a leak gap 54 between the inner cylindrical surface of the cylinder 52 and the outer periphery of the plunger 51.

[0008] Incidentally, in a hydraulic chain tensioner of the type shown in Figure 14, which is provided with an assist spring 56 that presses against the end of the plunger 51 inserted into the cylinder 52 in addition to the return spring 55 in order to supplement the spring force of the return spring 55 that presses against the end of the plunger 51 protruding from the cylinder 52, when air gets mixed in with the hydraulic oil in the pressure chamber 50, it takes time for the air to be expelled from the pressure chamber 50, and the damping force may remain reduced for a long period of time.

[0009] The inventors of the present application investigated the reason why it takes so long for air to be expelled from the pressure chamber 50 in a hydraulic chain tensioner of the type having an assist spring 56 that presses the insertion end of the plunger 51 into the cylinder 52, as shown in Figure 14, and found that the cause is air (air bubbles) becoming entangled in the wire that makes up the assist spring 56, hindering the axial movement of the air.

[0010] That is, as shown in FIG. 14 , the assist spring 56 that presses the insertion end of the plunger 51 into the cylinder 52 is a coil spring formed by spirally winding a metal wire and is arranged coaxially within the cylinder 52. Also, as shown in FIG. 15 , on the inner periphery of the cylinder 52, a cylindrical surface 58 having the same inner diameter as the inner periphery cylindrical surface 57 that forms the leak gap 54 extends axially toward the closed end of the cylinder 52 (to the left in the figure) relative to the leak gap 54. The radial width of the gap between the outer periphery of the assist spring 56 and the inner periphery cylindrical surface 58 of the cylinder 52 is less than 0.5 mm. Here, as shown in FIG. 14 , if air is mixed into the hydraulic oil in the pressure chamber 50, some of the air accumulates along the inner periphery of the cylinder 52, and the air (air bubbles) become entangled in the wire that constitutes the assist spring 56, thereby hindering the axial movement of the air. Therefore, it was found that the air accumulated along the inner periphery of the cylinder 52 does not reach the leak gap 54 easily, and it takes time for the air to be discharged.

[0011] Furthermore, if the leak gap 54 is set small (for example, if the radial width of the leak gap 54 is set to about 30 μm or less), there is also the problem that it takes time to exhaust the air that has accumulated along the inner circumference of the cylinder 52 to the outside through the leak gap 54.

[0012] The problem to be solved by this invention is to improve the ability to discharge air that has entered a pressure chamber in a hydraulic chain tensioner having a coil spring that presses the insertion end of a plunger into a cylinder. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a hydraulic chain tensioner having the following configuration. [Configuration 1] a cylinder having a closed end at one axial end and an open end at the other axial end; a plunger supported axially slidably on an inner peripheral cylindrical surface formed on the inner periphery of the cylinder; a pressure chamber surrounded by the cylinder and the plunger; an oil supply passage for supplying hydraulic oil to the pressure chamber; a check valve provided at an end of the oil supply passage on the pressure chamber side, the check valve allowing hydraulic oil to flow only from the oil supply passage side to the pressure chamber side; a leakage gap formed between the inner peripheral cylindrical surface of the cylinder and the outer periphery of the plunger; a coil spring arranged coaxially within the cylinder so as to press an insertion end of the plunger into the cylinder, In a hydraulic chain tensioner used in an orientation in which the direction in which the plunger protrudes from the cylinder is upward relative to the horizontal, a hydraulic chain tensioner characterized in that an air accommodating recess is formed in at least a portion of the inner circumference of the cylinder facing the upper side of the coil spring, the air accommodating recess being recessed radially outward relative to the radial position of the inner cylindrical surface and axially adjacent to the leak gap.

[0014] With this configuration, an air accommodating recess is formed in the inner periphery of the cylinder, at least in a portion facing the upper side of the coil spring, that is recessed radially outward relative to the radial position of the inner cylindrical surface that forms the leak gap. This provides a wide radial space between the outer periphery of the coil spring and the portion of the inner periphery of the cylinder that faces the upper side of the coil spring. This prevents air that accumulates along the inner periphery of the cylinder from becoming entangled with the wire that makes up the coil spring, allowing it to move smoothly in the axial direction. Furthermore, because the air accommodating recess is formed axially adjacent to the leak gap, air that accumulates along the inner periphery of the cylinder can smoothly travel along the air accommodating recess and reach the leak gap. This allows air that accumulates along the inner periphery of the cylinder to be smoothly discharged.

[0015] [Configuration 2] 2. The hydraulic chain tensioner according to claim 1, wherein the air accommodating recess is an annular recess formed by recessing the entire inner periphery of the cylinder radially outward.

[0016] By adopting this configuration, the inner periphery of the cylinder is recessed radially outward not only in the portion of the inner periphery facing the upper side of the coil spring, but also around the entire circumference, thereby making it possible to reduce the weight of the cylinder.

[0017] [Configuration 3] 2. The hydraulic chain tensioner according to claim 1, wherein the air accommodating recess is a recessed groove extending in the axial direction in a portion of the inner periphery of the cylinder that faces an upper side of the coil spring.

[0018] With this configuration, only the portion of the inner circumference of the cylinder that faces the upper side of the coil spring is recessed radially outward to form the air-accommodating recess, and the remaining portion can be a cylindrical surface with the same inner diameter as the inner cylindrical surface that forms the leak gap. This allows a large area to be secured for the surface of the inner circumference of the cylinder that supports the outer circumference of the plunger, making it possible to effectively prevent wear on the inner circumference of the cylinder due to the radial force received by the end of the plunger protruding from the cylinder.

[0019] [Configuration 4] 4. The hydraulic chain tensioner according to configuration 3, wherein the groove has a cross section perpendicular to the axial direction that is arc-shaped.

[0020] This configuration allows for easy and low-cost machining of the air accommodating recess. Specifically, the groove that forms the air accommodating recess is located on the inner periphery of the cylinder, closer to the closed end of the cylinder than the inner cylindrical surface that forms the leak gap. Therefore, for example, if a groove with a rectangular cross section perpendicular to the axial direction is used, it would be difficult to form the groove while avoiding the inner cylindrical surface, resulting in high machining costs. In contrast, if a groove with an arc-shaped cross section perpendicular to the axial direction is used, it can be formed by boring using an end mill, avoiding the inner cylindrical surface, resulting in low costs.

[0021] [Configuration 5] A hydraulic chain tensioner according to any one of configurations 1 to 4, wherein a radial air vent passage is provided at an end of the air accommodating recess that is closer to the open end of the cylinder, for discharging air that has accumulated in the air accommodating recess from the inner peripheral side to the outer peripheral side of the cylinder.

[0022] By adopting this configuration, air that has accumulated along the inner circumference of the cylinder can be discharged not only through the leak gap but also through the radial air vent passage, making it possible to quickly discharge air that has accumulated along the inner circumference of the cylinder to the outside.

[0023] [Configuration 6] 6. The hydraulic chain tensioner according to claim 5, wherein the radial air bleed passage is a thread gap formed between a threaded hole formed radially penetrating the cylinder and a male-threaded fastener that is threadedly engaged with the threaded hole.

[0024] [Configuration 7] The hydraulic chain tensioner according to configuration 5, wherein the radial air vent passage is a straight groove or a threaded groove formed on either the inner periphery of a cylindrical hole formed radially penetrating the cylinder or the outer periphery of a cylindrical member press-fitted into the cylindrical hole.

[0025] [Configuration 8] 8. The hydraulic chain tensioner according to any one of configurations 1 to 7, wherein the axial length of the leak gap is set to 5 mm or more.

[0026] [Configuration 9] 9. A hydraulic chain tensioner according to any one of configurations 1 to 8, wherein a distal air vent passage is provided at the end of the plunger protruding from the cylinder to discharge air that has become mixed in with the hydraulic oil in the pressure chamber. [Effects of the Invention]

[0027] The hydraulic chain tensioner of this invention has an air accommodating recess formed in the inner periphery of the cylinder, at least in a portion facing the upper side of the coil spring, that is recessed radially outward relative to the radial position of the inner cylindrical surface that forms the leak gap. This provides a large radial space between the outer periphery of the coil spring and the portion of the inner periphery of the cylinder that faces the upper side of the coil spring. This prevents air that accumulates along the inner periphery of the cylinder from becoming entangled with the wire that makes up the coil spring, allowing it to move smoothly in the axial direction. Furthermore, because the air accommodating recess is formed axially adjacent to the leak gap, air that accumulates along the inner periphery of the cylinder can smoothly travel along the air accommodating recess and reach the leak gap. This allows air that accumulates along the inner periphery of the cylinder to be smoothly discharged. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a front view showing a chain transmission device incorporating a hydraulic chain tensioner according to a first embodiment of the present invention. [Figure 2] Cross-sectional view along line II-II in Figure 1 [Figure 3] Cross-sectional view along line III-III in Figure 2 [Figure 4] Cross-sectional view along line IV-IV in Figure 2 [Figure 5] An enlarged cross-sectional view of the cylinder in FIG. 3, showing the area around the portion facing the upper side of the coil spring. [Figure 6] FIG. 4 is a diagram showing a hydraulic chain tensioner according to a second embodiment of the present invention, corresponding to FIG. 3. [Figure 7] An enlarged cross-sectional view of the area around the radial air vent passage in Figure 6. [Figure 8] Cross-sectional view taken along line VIII-VIII in Figure 7 [Figure 9] FIG. 4 is a diagram showing a hydraulic chain tensioner according to a third embodiment of the present invention, corresponding to FIG. 3. [Figure 10] Cross-sectional view along line XX in Figure 9 [Figure 11] FIG. 8 is a diagram showing another example of the radial air vent passage shown in FIG. 7. [Figure 12]Cross-sectional view along line XII-XII in Figure 11 [Figure 13] FIG. 8 is a diagram showing still another example of the radial air vent passage shown in FIG. 7; [Figure 14] FIG. 4 is a diagram corresponding to FIG. 3 and showing a hydraulic chain tensioner of a comparative example that does not have an air receiving recess. [Figure 15] An enlarged cross-sectional view of the vicinity of the portion of the cylinder facing the upper side of the coil spring in Figure 14. DETAILED DESCRIPTION OF THE INVENTION

[0029] Figure 1 shows a chain transmission device incorporating a hydraulic 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 is connected to a sprocket 5 fixed to a camshaft 4 via a chain 6. The chain 6 transmits the rotation of the crankshaft 2 to the camshaft 4, and the rotation of the camshaft 4 opens and closes a valve (not shown) in a combustion chamber.

[0030] When the engine is running, the crankshaft 2 rotates in a constant direction (clockwise in the figure), and at this time, the side of the chain 6 that is pulled into the sprocket 3 as the crankshaft 2 rotates (the right side of the figure) is the tight side, and the side that is let out from the sprocket 3 (the 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 hydraulic chain tensioner 1 presses against the chain 6 via the chain guide 8.

[0031] As shown in Figure 2, the hydraulic chain tensioner 1 has a cylindrical cylinder 9 with one axial end closed and the other axial end open, and a plunger 10 inserted into the cylinder 9 so as to be slidable in the axial direction. The end of the plunger 10 protruding from the cylinder 9 presses against the chain guide 8.

[0032] The cylinder 9 is inserted into a tensioner mounting hole 12 in the engine cover 11 with its open end facing inside the engine cover 11. The tensioner mounting hole 12 is a through-hole that penetrates the engine cover 11 from the outer surface to the inner surface. A flange portion 13 is formed on the outer periphery of the cylinder 9. The flange portion 13 is fixed to the outer surface of the engine cover 11 with bolts 14 (see FIG. 4). As shown in FIG. 1, the cylinder 9 is mounted in a position where the plunger 10 protrudes from the cylinder 9 in a direction that is inclined upward from the horizontal.

[0033] As shown in Figure 2, the cylinder 9 is provided with an oil supply passage 16 that supplies hydraulic oil to a pressure chamber 15 surrounded by the cylinder 9 and plunger 10. The oil inlet of the oil supply passage 16 opens to a mating surface 17 of the flange portion 13 of the cylinder 9 where it meets the engine cover 11. The engine cover 11 is formed with an oil hole 18 that supplies hydraulic oil delivered from the engine's oil pump (not shown) to the hydraulic chain tensioner 1, and the oil hole 18 is connected to the oil inlet of the oil supply passage 16. A check valve 20 is provided at the end of the oil supply passage 16 on the pressure chamber 15 side.

[0034] The check valve 20 has a valve seat 21, a spherical valve element 23 that opens and closes a valve hole 22 formed axially through the valve seat 21 from the pressure chamber 15 side, and a retainer 24 that holds the valve element 23. The check valve 20 prevents hydraulic oil from flowing from the pressure chamber 15 side to the oil supply passage 16 side, and only allows hydraulic oil to flow from the oil supply passage 16 side to the pressure chamber 15 side. The outer periphery of the valve seat 21 is fitted into a cylindrical valve fitting surface 25 formed on the inner periphery of the end on the closed end side of the cylinder 9. The inner diameter of the valve fitting surface 25 is smaller than the inner diameter of an inner cylindrical surface 27 that forms a leak gap 26, which will be described later.

[0035] The plunger 10 is formed in a cylindrical shape with an open end inserted into the cylinder 9 and a closed end protruding from the cylinder 9. The outer periphery of the plunger 10 is supported by an inner cylindrical surface 27 formed on the inner periphery of the cylinder 9 so as to be slidable in the axial direction. A leak gap 26 is formed between the inner cylindrical surface 27 of the cylinder 9 and the outer periphery of the plunger 10, allowing hydraulic oil to leak from the pressure chamber 15 when the plunger 10 moves in the direction of being pressed into the cylinder 9. The leak gap 26 is a minute cylindrical gap with a radial width set in the range of 15 μm to 120 μm (preferably 15 μm to 30 μm). The axial length of the leak gap 26 is set to 5 mm or more. Note that if the axial length of the leak gap 26 is less than 5 mm, the hydraulic damping force will be too small, and it may not be possible to absorb the tension of the chain 6 (see FIG. 1).

[0036] A tip air vent passage 28 is provided at the end of the plunger 10 protruding from the cylinder 9 to discharge air mixed in with the hydraulic oil in the pressure chamber 15. The tip air vent passage 28 is a spiral gap formed between the inner periphery of a threaded hole 29 formed axially through the end of the plunger 10 protruding from the cylinder 9 and the outer periphery of a cylindrical plug 30 press-fitted into the threaded hole 29.

[0037] A female thread 31 is formed on the inner periphery of the plunger 10. A screw rod 33 having a male thread 32 on its outer periphery that threadably engages with the female thread 31 of the plunger 10 is incorporated into the pressure chamber 15. The screw rod 33 is inserted into the plunger 10 with one end housed within the plunger 10 and the other end protruding from the plunger 10. The end of the screw rod 33 protruding from the plunger 10 is supported by abutting against a valve seat 21 provided at the closed end of the cylinder 9.

[0038] The male thread 32 on the outer periphery of the screw rod 33 and the female thread 31 on the inner periphery of the plunger 10 are formed in a sawtooth shape in which the flank angle of the pressure side flank that receives pressure when a load is applied in the direction of pushing the plunger 10 into the cylinder 9 is larger than the flank angle of the play side flank on the opposite side.

[0039] A return spring 34 is incorporated between the end of the plunger 10 protruding from the cylinder 9 and the screw rod 33. One end of the return spring 34 is supported in the axial direction by the screw rod 33, and the other end of the return spring 34 presses the end of the plunger 10 protruding from the cylinder 9 via a spring seat 35. The plunger 10 is urged in the direction of protruding from the cylinder 9 by the pressure of this return spring 34.

[0040] A coil spring 36 is incorporated between the inserted end of the plunger 10 into the cylinder 9 and the closed end of the cylinder 9. The coil spring 36 is a cylindrical compression coil spring formed by spirally winding a metal wire. The coil spring 36 is arranged coaxially within the cylinder 9. One end of the coil spring 36 is supported in the axial direction by the valve seat 21 of the check valve 20, and the other end of the coil spring 36 presses against the inserted end of the plunger 10 into the cylinder 9. The coil spring 36 functions as an assist spring that supplements the spring force of the return spring 34.

[0041] As shown in FIGS. 3 and 5 , an air accommodating recess 37 is formed on the inner periphery of the cylinder 9. The air accommodating recess 37 is a portion of the inner periphery of the cylinder 9 facing at least the upper side of the coil spring 36, recessed radially outward relative to the radial position of the inner cylindrical surface 27. In this embodiment, it is an annular recess recessed radially outward along the entire inner periphery of the cylinder 9. The air accommodating recess 37 has a cylindrical inner surface with a constant inner diameter along the axial direction, which is larger than the inner diameter of the inner cylindrical surface 27. The radial distance between the outer periphery of the coil spring 36 and the inner surface of the air accommodating recess 37 is set to 1.0 mm or more (preferably 1.2 mm or more). The air accommodating recess 37 is formed axially adjacent to the closed end of the cylinder 9 (on the left side in the drawings) with respect to the leak gap 26 and extends axially to a portion of the inner periphery of the cylinder 9 facing radially outward from the valve seat 21.

[0042] Next, an example of the operation of this hydraulic chain tensioner 1 will be described.

[0043] 1 increases while the engine is running, the tension of the chain 6 causes the plunger 10 to move in a direction that pushes it into the cylinder 9, absorbing the tension of the chain 6. At this time, the volume of the pressure chamber 15 decreases as the plunger 10 moves, and hydraulic oil flows out of the cylinder 9 from the pressure chamber 15 through the leak gap 26 by the amount of the decreased volume. The viscous resistance of the hydraulic oil flowing through the leak gap 26 generates a damping force, causing the plunger 10 to move slowly. At this time, the pressure-side flank of the internal thread 31 on the inner periphery of the plunger 10 abuts against the pressure-side flank of the external thread 32 on the outer periphery of the screw rod 33. As the chain 6 vibrates, slippage between the pressure-side flanks of the internal thread 31 and the external thread 32 accumulates, gradually pushing the screw rod 33 into the plunger 10.

[0044] 1 decreases while the engine is running, the pressure of the hydraulic oil in the pressure chamber 15 shown in FIG. 3 and the biasing forces of the return spring 34 and coil spring 36 cause the plunger 10 to move in the direction of protruding from the cylinder 9, absorbing the slack in the chain 6 (see FIG. 1). At this time, the biasing force of the return spring 34 causes the play-side flank of the female thread 31 on the inner periphery of the plunger 10 to abut against the play-side flank of the male thread 32 on the outer periphery of the screw rod 33, and the screw rod 33 rotates relative to the plunger 10 due to slippage between the play-side flanks of the female thread 31 and the male thread 32.

[0045] When the engine is stopped, the tension in the chain 6 may increase depending on the stopping position of the camshaft 4 shown in Fig. 1. In this case, the chain 6 does not vibrate, so no slippage occurs between the pressure side flank of the female thread 31 on the inner periphery of the plunger 10 and the pressure side flank of the male thread 32 on the outer periphery of the screw rod 33 shown in Fig. 3, limiting the movement of the plunger 10 in the direction of being pushed into the cylinder 9. Therefore, when restarting the engine, the chain 6 shown in Fig. 1 is less likely to become loose, allowing for smooth engine starting.

[0046] During engine operation, a sudden drop in pressure in the pressure chamber 15 shown in FIG. 3 may cause air to separate from the hydraulic oil in the pressure chamber 15, or hydraulic oil containing air may be supplied to the pressure chamber 15 from the oil hole 18 shown in FIG. 2 through the oil supply passage 16, resulting in air being mixed into the hydraulic oil in the pressure chamber 15.

[0047] In this case, air that has accumulated inside the plunger 10 in the pressure chamber 15 shown in Figure 3 is discharged to the outside through a tip air vent passage 28 provided at the end of the plunger 10 that protrudes from the cylinder 9. Also, air that has accumulated along the inner periphery of the cylinder 9 in the pressure chamber 15 is discharged to the outside through a leak gap 26 between an inner cylindrical surface 27 of the cylinder 9 and the outer periphery of the plunger 10.

[0048] As shown in FIG. 3 , the hydraulic chain tensioner 1 has an air accommodating recess 37 recessed radially outward relative to the radial position of the inner cylindrical surface 27 in at least a portion of the inner periphery of the cylinder 9 facing the upper side of the coil spring 36. This provides a wide radial space between the outer periphery of the coil spring 36 and the portion of the inner periphery of the cylinder 9 facing the upper side of the coil spring 36. This prevents air (air bubbles) that accumulates along the inner periphery of the cylinder 9 from becoming entangled with the wire that makes up the coil spring 36, allowing it to move smoothly in the axial direction. Furthermore, because the air accommodating recess 37 is formed axially adjacent to the leak gap 26, air that accumulates along the inner periphery of the cylinder 9 can smoothly travel along the air accommodating recess 37 to the leak gap 26. This allows air that accumulates along the inner periphery of the cylinder 9 to be smoothly discharged.

[0049] Furthermore, this hydraulic chain tensioner 1 employs an annular recess as the air accommodating recess 37, recessed radially outward along the entire inner periphery of the cylinder 9, meaning that the inner periphery of the cylinder 9 is recessed radially outward along the entire periphery, not just the portion of the inner periphery facing the upper side of the coil spring 36. This makes the cylinder 9 lightweight. Furthermore, compared to the third embodiment described below, the air accommodating recess 37 can be manufactured more simply and at lower cost.

[0050] 6 to 8 show a hydraulic chain tensioner 1 according to a second embodiment of the present invention. The second embodiment is different from the first embodiment in that it adds a radial air bleed passage 38, but otherwise has the same configuration as the first embodiment. Therefore, parts corresponding to those in the first embodiment are given the same reference numerals and their description will be omitted.

[0051] As shown in FIG. 6 , a radial air vent passage 38 is provided at the end of the air accommodating recess 37 closer to the open end of the cylinder 9, and discharges air accumulated in the air accommodating recess 37 from the inner circumferential side to the outer circumferential side of the cylinder 9. As shown in FIG. 7 , the radial air vent passage 38 is a spiral gap formed between a threaded hole 39 formed radially penetrating the cylinder 9 and a male-threaded fastener 40 that threadably engages with the threaded hole 39. Also, as shown in FIG. 8 , a flat surface 41 is formed on the outer periphery of the cylinder 9 at a position that includes the end opening of the threaded hole 39. As shown in FIGS. 6 and 7 , an air discharge gap 42 is formed between the flat surface 41 and the inner periphery of the tensioner mounting hole 12, and communicates the outer circumferential side end of the radial air vent passage 38 with the engine compartment inside the engine cover 11.

[0052] As shown in Figure 7, this hydraulic chain tensioner 1 can discharge air that has accumulated along the inner periphery of the cylinder 9 not only through the leak gap 26 but also through the radial air vent passage 38. This makes it possible to quickly discharge air that has accumulated along the inner periphery of the cylinder 9 to the outside. Other functions and effects are the same as those of the first embodiment.

[0053] 9 and 10 show a hydraulic chain tensioner 1 according to a third embodiment of the present invention. The third embodiment differs from the second embodiment only in the configuration of the air accommodating recess 37, and the other configurations are the same as those of the second embodiment. Therefore, parts corresponding to those of the second embodiment are given the same reference numerals and descriptions thereof will be omitted.

[0054] 9, an air accommodating recess 37 is formed on the inner periphery of the cylinder 9. The air accommodating recess 37 is a portion of the inner periphery of the cylinder 9 facing the upper side of the coil spring 36 that is recessed radially outward relative to the radial position of the inner periphery cylindrical surface 27, and in this embodiment, the portion of the inner periphery of the cylinder 9 facing the upper side of the coil spring 36 is a recessed groove that extends in the axial direction.

[0055] As shown in Figure 10, the groove that forms the air accommodating recess 37 is a groove that has an arc-shaped cross section perpendicular to the axial direction. The center of the arc of the groove that forms the air accommodating recess 37 is eccentric to the upper side with respect to the center of the inner cylindrical surface 27 (see Figure 9). The radius of curvature of the arc of the groove that forms the air accommodating recess 37 is smaller than the inner radius of the inner cylindrical surface 27, and is set to 75% or less of the inner radius of the inner cylindrical surface 27.

[0056] As shown in FIG. 9, the air accommodating recess 37 is formed axially adjacent to the leak gap 26 on the closed end side of the cylinder 9 (on the left side in the figure), and extends axially to a portion of the inner periphery of the cylinder 9 facing the radially outer side of the valve seat 21.

[0057] As shown in Figure 10, in this hydraulic chain tensioner 1, only the portion of the inner periphery of the cylinder 9 that faces the upper side of the coil spring 36 is recessed radially outward to form an air accommodating recess 37, and the remaining portion is a cylindrical surface 43 of the same inner diameter as the inner cylindrical surface 27 that forms the leak gap 26, as shown in Figure 9. This makes it possible to ensure a large area for the surface of the inner periphery of the cylinder 9 that supports the outer periphery of the plunger 10, making it possible to effectively prevent wear on the inner periphery of the cylinder 9 due to the radial force that is applied when the end of the plunger 10 protruding from the cylinder 9 comes into contact with the chain guide 8.

[0058] Furthermore, as shown in FIG. 10 , in this hydraulic chain tensioner 1, the groove that forms the air accommodating recess 37 has an arc-shaped cross section perpendicular to the axial direction, which allows the air accommodating recess 37 to be easily machined and is low-cost. That is, as shown in FIG. 9 , the groove that forms the air accommodating recess 37 is located on the inner periphery of the cylinder 9 closer to the closed end of the cylinder 9 (to the left in the figure) than the inner cylindrical surface 27 that forms the leak gap 26. Therefore, for example, if a groove that forms the air accommodating recess 37 has a rectangular cross section perpendicular to the axial direction, it would be difficult to form the groove while avoiding the inner cylindrical surface 27, resulting in high machining costs. In contrast, if a groove that forms the air accommodating recess 37 has an arc-shaped cross section perpendicular to the axial direction, as shown in FIG. 10 , it would be possible to form the groove by boring using an end mill, avoiding the inner cylindrical surface 27, thereby reducing costs.

[0059] In addition, this hydraulic chain tensioner 1 provides the same effects as the first and second embodiments.

[0060] 11 and 12 show modified examples of the radial air vent passage 38. In Fig. 11, a cylindrical member 45 is press-fitted into a cylindrical hole 44 formed radially penetrating the cylinder 9. A straight groove that constitutes the radial air vent passage 38 is formed on the inner periphery of the cylindrical hole 44. The straight groove extends parallel to the center line of the cylindrical hole 44. Here, as shown in Fig. 12, the straight groove is formed on the inner periphery of the cylindrical hole 44, but the straight groove may be formed on the outer periphery of the cylindrical member 45 instead of on the inner periphery of the cylindrical hole 44.

[0061] Figure 13 shows another modified example of the radial air vent passage 38. In Figure 13, a cylindrical member 45 is press-fitted into a cylindrical hole 44 formed by radially penetrating the cylinder 9. A thread groove is formed on the inner periphery of the cylindrical hole 44, which constitutes the radial air vent passage 38. Here, the thread groove is formed on the inner periphery of the cylindrical hole 44, but the thread groove may be formed on the outer periphery of the cylindrical member 45 instead of the inner periphery of the cylindrical hole 44.

[0062] In the above embodiment, an example was given in which the hydraulic chain tensioner 1 was incorporated into a chain transmission device that transmits the rotation of the crankshaft 2 to the camshaft 4. However, the hydraulic chain tensioner 1 can also be incorporated into chain transmission devices that transmit the rotation of the crankshaft 2 to accessories such as an oil pump, a water pump, or a supercharger, a chain transmission device that transmits the rotation of the crankshaft 2 to a balancer shaft, or a chain transmission device that connects the intake cam and exhaust cam of a twin-cam engine.

[0063] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0064] 1 Hydraulic Chain Tensioner 9 cylinders 10 Plunger 15 Pressure Chamber 16 Fuel passage 20 Check valve 26 Leak gap 27 Inner cylindrical surface 28 Tip air vent passage 36 coil spring 37 Air receiving recess 38 Radial air vent passage 39 screw hole 40 Male thread parts 44 Cylindrical hole 45 Cylindrical member

Claims

1. A bottomed cylindrical cylinder (9) having one axial end as a closed end and the other axial end as an open end; a plunger (10) supported axially slidably on an inner peripheral cylindrical surface (27) formed on the inner periphery of the cylinder (9); a pressure chamber (15) surrounded by the cylinder (9) and the plunger (10); an oil supply passage (16) for supplying hydraulic oil to the pressure chamber (15); a check valve (20) provided at an end of the oil supply passage (16) on the pressure chamber (15) side, for allowing hydraulic oil to flow only from the oil supply passage (16) side to the pressure chamber (15) side; a leakage gap (26) formed between the inner peripheral cylindrical surface (27) of the cylinder (9) and an outer periphery of the plunger (10); a coil spring (36) arranged coaxially within the cylinder (9) so as to press the insertion end of the plunger (10) into the cylinder (9); In the hydraulic chain tensioner, the plunger (10) is used in an orientation in which the protruding direction from the cylinder (9) is upward relative to the horizontal, a hydraulic chain tensioner characterized in that an air accommodating recess (37) is formed in at least a portion of the inner circumference of the cylinder (9) facing an upper side of the coil spring (36), the air accommodating recess (37) being recessed radially outward with respect to the radial position of the inner cylindrical surface (27) and adjacent to the leak gap (26) in the axial direction.

2. 2. The hydraulic chain tensioner according to claim 1, wherein the air accommodating recess (37) is an annular recess formed by recessing the entire inner periphery of the cylinder (9) radially outward.

3. 2. The hydraulic chain tensioner according to claim 1, wherein the air accommodating recess (37) is a groove extending in the axial direction on an inner periphery of the cylinder (9) in a portion facing an upper side of the coil spring (36).

4. 4. The hydraulic chain tensioner according to claim 3, wherein the groove has a cross-sectional shape perpendicular to the axial direction that is arcuate.

5. 5. The hydraulic chain tensioner according to claim 1, wherein a radial air vent passage (38) for discharging air accumulated in the air accommodating recess (37) from the inner periphery side to the outer periphery side of the cylinder (9) is provided at an end of the air accommodating recess (37) that is closer to the open end of the cylinder (9).

6. 6. The hydraulic chain tensioner according to claim 5, wherein the radial air bleed passage (38) is a thread gap formed between a threaded hole (39) formed radially penetrating the cylinder (9) and a male-threaded part (40) threadedly engaged with the threaded hole (39).

7. 6. The hydraulic chain tensioner according to claim 5, wherein the radial air bleed passage (38) is a straight groove or a threaded groove formed on either an inner periphery of a cylindrical hole (44) formed radially penetrating the cylinder (9) or an outer periphery of a columnar member (45) press-fitted into the cylindrical hole (44).

8. 5. The hydraulic chain tensioner according to claim 1, wherein the axial length of the leak gap (26) is set to 5 mm or more.

9. 5. A hydraulic chain tensioner as set forth in claim 1, wherein a tip air bleed passage (28) for discharging air mixed in with the hydraulic oil in the pressure chamber (15) is provided at an end of the plunger (10) protruding from the cylinder (9).

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