GB2308420A

GB2308420A - Hydraulic Tensioner

Info

Publication number: GB2308420A
Application number: GB9621678A
Authority: GB
Inventors: Hiroshi Hayafune; Shigekazu Fukuda; Tadasu Suzuki
Original assignee: Tsubakimoto Chain Co
Current assignee: Tsubakimoto Chain Co
Priority date: 1995-12-20
Filing date: 1996-10-17
Publication date: 1997-06-25
Also published as: DE19653066A1; JPH09177907A; GB9621678D0; KR970046328A; KR100238000B1

Description

1 HYDRAULIC LIFT-UP TENSIONER 2308420 The present invention relates to a

hydraulic lift-up tensioner for applying a tension to a power transmission chain from below.

Conventionally, a chain power transmission mechanism is used to transmit rotation of a crankshaft to a camshaft or camshafts of an engine. FIG. 2 shows one example of such chain power transmission mechanism in which a chain 21 is driven by a drive sprocket 20 attached to a crankshaft, not shown, and rotates a driven sprocket 22 attached to a camshaft, not shown, so that rotation of the crankshaft is transmitted to the camshaft.

The camshaft has a cam sprocket attached thereto and rotatable integrally with the driven sprocket 22 to rotate a cam sprocket 25 attached to another camshaft, not shown, via the chain 24.

The chain 24 extending between the cam sprocket 23 and the cam sprocket 25 for interlocking the two camshafts has an upper running portion against which a shoe 27 of a hydraulic lift-up tensioner 26 secured to a part of the engine is urged from below to apply an appropriate tension to the chain 24. A lower running portion of the chain 24 is guided by sliding contact with a fixed or stationary shoe 28 attached to a lower end of the hydraulic lift-up tensioner 26.

FIG. 3 is a cross-sectional view showing an internal structure of the hydraulic lift-up tensioner 26. The hydraulic lift-up tensioner 26 is used with its body 29 attached to a mount member, not shown, of the engine. The tensioner body 29 is formed with a plunger chamber 31 opening at an upper end. A hollow plunger 30 is slidably fitted in -the plunger chamber 31 and has an upper end to which the shoe 27 is attached.

The plunger 31 includes an orifice plate 32 fixedly mounted therein. A spring 33 is disposed between a lower end face of the orifice plate 32 and a bottom surface of 2 the plunger chamber 31. By the spring 33 the plunger 30 is urged upwardly to force the shoe 27 against the chain 24.

A lower portion of the plunger chamber 31 and an internal space of the plunger 30 closed from the outside by the orifice plate 32 jointly form a high pressure chamber 34. The tensioner body 29 has an oil passage 36 communicating with the high pressure chamber 34 via a check valve 35.

With the hydraulic lift-up tensioner 26 thus arranged, an oil is supplied into the tensioner body 26 from the outside thereof via the oil passage 36. The oil flows into the high pressure chamber 34 via the check valve 35 and fills up the high pressure chamber 34.

In the case where an impact force is applied from the chain 24 side to the shoe 27, the plunger 30 is forced into the plunger chamber 31 whereupon the pressure in the high pressure chamber 31 is increased and thus closes the check valve 30. As a consequence, the oil in the high pressure chamber 25 is forced out to the exterior via bypass passages 32A formed in the orifice plate 32. The oil, as it passes through the bypass passages 32A, encounters a flow resistance so that the impact force can be dampened with concurrent attenuation of oscillation of the plunger 30 obtained.

The hydraulic lift-up tensioner of the foregoing construction, however, has a drawback that since the oil is supplied via the check valve to the high pressure chamber from below, if the engine is stopped for a long period of time, the oil filled in the high pressure chamber can leak out downwards, by its own weight, through a small gap or clearance in the check valve because during such time period, no hydraulic pressure is built up in the oil passage due to stop of an external oil supply pump.

Thus, the high pressure chamber is'liable to collect air. However, since the air collected in the high pressure chamber is released from the bypass passages in the orifice plate, it is impossible to improve the fluid-tightness of 3 the bypass passage. Consequently, difficulties arise in that the ability of dampening an impact force applied from the chain side and the ability of attenuating vibrations cannot be improved, and the manufacturing cost is increased due to the necessity of using an expensive orifice plate having hard-to-work bypass passages.

It is accordingly an object of the present invention to overcome the foregoing problems and provide a hydraulic lift-up tensioner which is free from oil leak from the high pressure chamber, can readily remove air entrained into supply oil, is simple in construction, and can be manufactured at a low cost.

According to the present invention, there is provided a hydraulic lift-up tensioner comprising a plunger including a shoe provided at an upper end thereof for sliding engagement with a chain, the plunger being vertically slidably fitted in a plunger chamber formed in a tensioner body; the plunger including a check valve disposed at a lower end thereof and further having an internal oil reservoir chamber held in fluid-communication with the check valve, and a vent hole interconnecting an upper portion of the oil reservoir chamber to the outside of the plunger; and the tensioner body having an oil passage for supply an oil to the oil reservoir chamber through an oil supply hole formed in a sidewall of the plunger, there being defined between a bottom portion of the plunger chamber and the lower end of the plunger a high pressure chamber in which a spring is disposed for urging the plunger upwardly.

Preferably, when an oil is supplied from an external oil supply source into an oil passage in the tensioner body, the oil flows into the oil reservoir chamber via an oil supply hole in the sidewall of the plunger. In this instance, air inside the oil reservoir chamber is displaced upwardly by the oil and expelled from the vent hole to the outside of the plunger. Thus, the oil reservoir chamber is filled up with the oil. A part of the oil flows downwardly 4 through the check valve and moves into the high pressure chamber. Air inside the high pressure chamber either escapes to the oil reservoir chamber through the check valve being open, or is discharged to the outside of the tensioner body through a clearance between an outer peripheral surface of the plunger and an inner peripheral surface of the plunger chamber. Thus, the high pressure chamber is filled up with the oil.

In this condition, if the plunger is thrust down by an impact force applied from the chain to the shoe, the pressure in the high pressure chamber increases and thus closes the check valve. The oil trapped in the high pressure chamber is forced out to the outside of the tensioner body through a clearance between the outer peripheral surface of the plunger and the inner peripheral surface of the plunger chamber. In this instance, the oil encounters a flow resistance by means of which the impact force is dampened, and vibration of the plunger caused by the impact force is attenuated.

When the chain becomes loose, the plunger is lifted up by the spring, thereby takes up a slack of the chain. In this instance, due to a pressure drop built up in the high pressure chamber by a reduction in volume of the high pressure chamber, the check valve is opened and, hence, the high pressure chamber is replenished with oil coming from the reservoir chamber through the check valve. The oil reservoir chamber is also replenished with oil supplied from the external oil supply source through the oil passage in the tensioner body and the oil supply hole in the plunger.

Even if air enters the high pressure chamber, the air is expelled to the outside of the tensioner body through the clearance extending upwardly from the lower end face of the plunger and defined between the outer peripheral surface of the plunger and the inner peripheral surface of the plunger chamber.

is An embodiment of the present invention will be described hereinafter with reference to the drawings, in which:

Fig. 1 is a cross-sectional view showing one embodiment of a hydraulic lift-up tensioner according to the present invention; Fig. 2 is a view showing one example of a chain power transmission device in which a hydraulic lift-up tensioner is used; and Fig. 3 is a cross-sectional view showing one example of conventional hydraulic lift-up tensioner.

The hydraulic lift-up tensioner 1 has a tensioner body 3 adapted to be attached to a mount member provided near a chain 2 of an engine.

The tensioner body 3 has a plunger chamber 4 open upwardly. A plunger 5 is vertically slidably fitted in the plunger chamber 4. The plunger 5 has an upper portion exposed to the outside of the plunger chamber 4, and at an upper end thereof, the plunger 5 is attached to a shoe 6 which is held in sliding contact with an underside of the chain 2. The exposed upper portion of the plunger 5 has a stopper pin 7 implanted in an outer peripheral surface thereof The stopper pin 7 has a distal end portion slidably received in a vertical elongated guide hole 8 in the tensioner body 3 so as to limit the range of vertical sliding movement of the plunger 5 and prevent rotation of the plunger 5.

The plunger 5 has an oil reservoir chamber 9 formed therein, and an oil supply hole 10 drilled in a sidewall of the plunger 5 surrounding the oil reservoir chamber 9. The oil supply hole 10 opens at one end to the outer peripheral surface of the plunger 5 in which an annular oil groove 11 is formed. The tensioner body 3 further has an oil passage 12 opening at one end to an inner peripheral surf ace of the plunger chamber 4 at a position confronted with the oil groove 11. The oil groove 11 has a vertical extent or width large enough to keep the oil supply hole 10 in f luid 6 communication with the oil passage 12 throughout the range of vertical movement of the plunger 5. The oil groove 11 may be f ormed in the inner peripheral surf ace of the plunger chamber 4 of the tensioner body 3.

The oil passage 12 is connected with an oil supply source, not shown, disposed outside the tensioner body 3, so that an oil is supplied to the oil reservoir chamber 9 successively through the oil passage 12, the oil groove 11, and the oil supply hole 10.

The plunger 5 is equipped with a check valve 13 disposed at a lower end thereof and including a ball as a valve element. The bottom of the plunger chamber 4 and the lower end of the plunger 5 define therebetween a high pressure chamber 14. The oil stored in the oil reservoir chamber 9 is permitted to flow through the check valve 13 into the high pressure chamber 14.

A spring 15 is disposed in the high pressure chamber 14 and acts between the bottom of the plunger chamber 4 and the lower end face of the plunger 5 to urge the plunger 5 upwardly whereby the shoe 6 attached to the upper end of the plunger 5 is forced against the chain 2.

The plunger 5 has a vent hole 16 connected at one end to an upper end of the oil reservoir chamber 9 and opening at the opposite end to an upper end face of the plunger 5. The shoe 6 attached to the upper end of the plunger 5 has a through-hole 17 held in fluid communication with the vent hole 16. The tensioner body 3 has a lower end portion to which is attached a fixed or stationary shoe 18 for sliding contact with a lower running portion of the chain 2 opposite to the upper running portion slidably engaged with the shoe 6.

With the construction described above, when the oil is supplied from the oil passages 12 into the oil reservoir chamber 9, a portion of the supplied oil flows into the high pressure chamber 14 through the check valve 13. In this instance, air which has been trapped in the high pressure chamber 14 is replaced with the oil coming from 7 the oil reservoir chamber 9, and the replaced air either flows into the oil reservoir chamber 9 through the check valve 13, or is expelled to the exterior side through a clearance between the outer peripheral surface of the plunger 5 and the inner peripheral surface of the plunger chamber 4. In the oil reservoir chamber 9 the excess air rises above the oil and then is released from the oil reservoir chamber 9 to the outside of the tensioner body 3 through the vent hole 16 and the through-hole 17.

When the shoe 6 is subjected to an impact force applied thereto from the chain 2 side, the plunger 5 is forced into the plunger chamber 4 against the force of the spring 15. With this movement of the plunger 5, the pressure in the high pressure chamber 14 is increases whereupon the check valve 13 fixed to the lower end of the plunger 5 is closed. The oil thus trapped in the high pressure chamber 14 is forced to move upwardly through a small clearance between the outer peripheral surface of the plunger 5 and the inner peripheral surface of the plunger chamber 4 and expelled from the upper open end of the plunger chamber 4 to the outside of the tensioner body 3. The oil, as it passes through the clearance, encounters a severe flow resistance by means of which the impact force is dampened and vibration of the plunger 5 is attenuated.

If the chain 2 becomes loose, a slack of the chain 2 can be removed by the shoe 6 as the plunger 5 is lifted up by the force of the spring 15. Since the upward movement of the plunger 5 increases the volume of the high pressure chamber 14, a pressure drop is built up in the high pressure chamber 14. Thus the check valve 13 is opened, allowing the oil to flow from the oil reservoir chamber 9 into the high pressure chamber 14 to replenish the high pressure chamber 14.

The oil reservoir chamber 9 is replenished with oil supplied thereinto from the non-illustrated oil supply source via the oil passages 12 and the oil supply hole 10 in the side wall of the plunger 5.

8 If air enters the high pressure chamber 14, the air automatically rises up above the oil. Accordingly, the air is guided by the lower end face of the plunger 5 into the clearance between the outer peripheral surface of the plunger 5 and the inner peripheral surface of the plunger chamber 4 and smoothly discharged therefrom to the outside of the tensioner body 3.

In the embodiment described above, the hydraulic lift-up tensioner is used with a chain provided inside the engine room. However, the hydraulic lift-up tensioner of this invention may be used in combination with a power transmission chain used in another mechanical devices.

According to the arrangement of the illustrated embodiment, a stationary shoe 18 is attached to a lower end of the tensioner body 3 for sliding engagement with the chain 2. The stationary shoe 18 may be omitted in which instance the tensioner includes a movable shoe 6, only.

As described above, the high pressure chamber is located below the plunger, and the plunger has an internal oil reservoir chamber formed such that an oil can be supplied from the oil reservoir chamber to the high pressure chamber via a check valve disposed at a lower end of the plunger. With this arrangement, leakage of oil from the high pressure chamber can be avoided, and the tensioner can operate reliably even when it is activated after a long-term suspension of oil supply.

since air coming from the oil passage into the oil reservoir chamber moves upwards and then is released from the exterior via the vent hole formed at the upper end of the plunger, the air is unlikely to enter the high pressure chamber. Even if the air is trapped in the high pressure chamber, the air is smoothly expelled to the outside of the tensioner body through the clearance extending from the lower end face of the plunger between the outer peripheral surface of the plunger and the inner peripheral surface of the plunger chamber. Thus, the air has no adverse effect on the operation of the tensioner.

9 Accordingly, there is no need of providing a hard-to-work and expensive orif ice plate which is required by the conventional lift-up tensioner. Thus, a considerably reduction in manufacturing cost is possible. The high pressure chamber has no venting orifice and hence has an improved fluidtightness which will improve the ability of dampening the impact force applied from the chain to the plunger and vibration of the plunger.

Claims

1. A hydraulic lift-up tensioner comprising a plunger including a shoe provided at an upper end thereof for sliding engagement with a chain, the plunger being vertically slidably fitted in a plunger chamber formed in a tensioner body; the plunger including a check valve disposed at a lower end thereof and further having an internal oil reservoir chamber held in fluid-communication with the check valve, and a vent hole interconnecting an upper portion of the oil reservoir chamber to the outside of the plunger; and the tensioner body having an oil passage for supply an oil to the oil reservoir chamber through an oil supply hole formed in a sidewall of the plunger, there being defined between a bottom portion of the plunger chamber and the lower end of the plunger a high pressure chamber in which a spring is disposed for urging the plunger upwardly.

2. A tensioner according to claim 1, wherein the check valve is arranged to open to allow the flow of oil from the internal oil reservoir to the high pressure chamber when the pressure in the high pressure chamber drops below a certain level.

3. A tensioner according to claim 1 or claim 2, wherein an oil flow resistance path between the high pressure chamber and the internal oil reservoir is formed by the clearance between the external surface of the plunger and the plunger chamber.

4. A hydraulic lift-up tensioner substantially as described with reference to Fig. 1.