Chain tensioner

To provide a chain tensioner capable of constantly applying an appropriate pressing force under any situations including high-speed, high-load operation, at the start of an engine, and normal range operation, without an increase in size or amount of oil consumption. A check valve unit 150 is disposed between an oil pressure chamber 101 and an oil supply part 103. A second oil pressure chamber 102 is formed between an outer circumferential surface of a plunger 120 and a cylindrical surface 113 of a plunger bore 111, into which oil leaking from the oil pressure chamber 101 flows and whose volume increases as the plunger 120 retracts. Further provided is a relief valve unit 130 that releases oil when the pressure of the second oil pressure chamber 102 reaches or exceeds a predetermined high level.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chain tensioner that includes a tensioner body having a cylindrical plunger bore with one open end, a cylindrical plunger slidably inserted in the plunger bore, and biasing means accommodated inside an oil pressure chamber formed between the plunger bore and the plunger such as to freely expand and contract and to urge the plunger in an advancing direction, and that maintains appropriate tension of a chain.

2. Description of the Related Art

It has been common practice to use a chain tensioner for maintaining appropriate tension of a chain. For example, a chain guide mechanism has been known, which slidably guides, by means of a guide shoe, a transmission chain such as an endless roller chain passing over respective sprockets of a crankshaft and a cam shaft inside an engine room, and which uses a chain tensioner to press a pivoting chain guide having the guide shoe to maintain appropriate tension.

A chain guide mechanism is configured as shown inFIG. 5, for example, wherein a pivoting chain guide G1and a fixed chain guide G2guide an endless timing chain CH passing over a drive sprocket S1of a crankshaft and a pair of driven sprockets S2and S3of cam shafts inside an engine room.

The fixed chain guide G2is fixed in position in the engine room, with two mounting shafts B1and B2, while the pivoting chain guide G1is attached such as to be pivotable around the mounting shaft B0in the plane in which the timing chain CH runs in the engine room.

A chain tensioner500presses the pivoting chain guide G1and thereby maintains the tension of the timing chain CH at an appropriate level as well as reduces its vibration.

The known chain tensioner500used in such a chain guide mechanism includes, for example, as shown schematically inFIG. 6, a tensioner body510having a cylindrical plunger bore511with one open end, a cylindrical plunger520inserted in the plunger bore511to freely slide against a cylindrical surface513of the plunger bore511, and means for biasing the plunger520in an advancing direction from the plunger bore511.

The biasing means is formed by a coil spring540accommodated inside a cylindrical recess521in the cylindrical plunger520and compressed between the plunger and a bottom part512of the plunger bore511.

Oil is supplied from an oil supply hole514formed in the plunger bore511, so that an oil pressure chamber501formed between the plunger bore511and the plunger520is filled with the oil, which oil urges the plunger520in the advancing direction. A check valve550(schematically shown as a check ball) stops the oil from flowing out from the oil supply hole514.

As the plunger520thereby reciprocates, the oil flows through a small gap between the plunger520and the plunger bore511, and the flow resistance provides the damping effect of slowing down the reciprocal movement of the plunger520.

SUMMARY OF THE INVENTION

In such a chain tensioner, because of the worry that rattling may occur due to looseness in the chain during high-speed, high-load operation, or at the start of the engine when the hydraulic damping force does not effectively act due to entrapped air or the like, it is desirable that the biasing means be designed to have a large spring load, or the plunger be made with a large diameter. However, the biasing means with a large spring load would press the chain more than necessary during normal range operation, and the increased chain tension would deteriorate friction properties between the chain and its running surface, and would further lead to an increased noise and poorer engine fuel economy.

On the other hand, increasing the plunger diameter would require a larger design for the chain tensioner itself, and bring up problems such as larger installation space being required, and increased weight and cost.

In one known chain tensioner, to mitigate these problems, an orifice is provided for releasing oil in the oil pressure chamber (high pressure oil chamber8) to the outside with a predetermined flow resistance so as to eject the air that has been entrapped earlier after the start of the engine, so that rattling or looseness of the chain is reduced (see, Japanese Patent Application Laid-open No. 2000-240744, etc).

However, with the technique described in Japanese Patent Application Laid-open No. 2000-240744, the hydraulic damping effect does not act immediately after the start of the engine, and when the biasing means has a small spring load, the preventive effects were limited.

Moreover, because the oil is released to the outside from the orifice and more oil is consumed, the oil pump performance needed to be enhanced.

Furthermore, this technique was not particularly effective for the rattling or looseness of the chain during high-speed, high-load operation.

It is an object of the present invention to solve these problems and to provide a chain tensioner capable of constantly applying an appropriate pressing force under any situations including high-speed, high-load operation, at the start of the engine, and normal range operation, without an increase in size or amount of oil consumption.

The chain tensioner of the present invention includes: a tensioner body having a cylindrical plunger bore with one open end; a cylindrical plunger slidably inserted in the plunger bore; biasing means accommodated inside an oil pressure chamber formed between the plunger bore and the plunger such as to freely expand and contract and to urge the plunger in an advancing direction; a check valve unit disposed between the oil pressure chamber and an oil supply part; a second oil pressure chamber formed between an outer circumferential surface of the plunger and a cylindrical surface of the plunger bore, into which oil leaking from the oil pressure chamber flows and whose volume increases as the plunger retracts; and a relief valve unit that releases oil when pressure of the second oil pressure chamber reaches or exceeds a predetermined high level. The problems described above are thereby solved.

The chain tensioner according to claim1includes a second oil pressure chamber formed between an outer circumferential surface of the plunger and a cylindrical surface of the plunger bore, into which oil leaking from the oil pressure chamber flows and whose volume increases as the plunger retracts, and a relief valve unit that releases oil when pressure of the second oil pressure chamber reaches or exceeds a predetermined high level. In or below the normal operation range, the pressure of the second oil pressure chamber does not exceed the valve opening pressure of the relief valve unit. When the plunger advances, a flow of oil from the second oil pressure chamber back into the oil pressure chamber is created. Thus a hydraulic damping force acts when the plunger advances, which force acts to reduce the pressing force of the biasing means on the plunger in the advancing direction.

Therefore, even when the spring load of the biasing means is set high, in the normal operation range, the plunger is prevented from being advanced with an unnecessarily large force to push the chain with too much force and to increase the chain tension. Accordingly, the friction properties between the chain and its running surface are improved, and a noise increase or degradation of engine fuel economy are prevented.

At the start of the engine, the second oil pressure chamber and oil pressure chamber are not filled with oil and there is hardly any damping force acting between the second oil pressure chamber and the oil pressure chamber. Since there is no force acting to reduce the pressing force of the biasing means on the plunger in the advancing direction, rattling or looseness of the chain can be prevented with the biasing means designed to have a large spring load.

During high-speed, high-load operation, the pressure of the second oil pressure chamber is also high, which causes the relief valve unit to open. Therefore, no flow of oil from the second oil pressure chamber back into the oil pressure chamber is created, and no hydraulic damping force acts when the plunger advances. Since there is no force acting to reduce the pressing force of the biasing means on the plunger in the advancing direction, the biasing means designed to have a large spring load can apply a sufficient pressing force.

As can be seen, this allows the biasing means to have a large spring load, so that the plunger diameter need not be increased. Therefore, the tensioner can be made smaller, and offers a higher degree of freedom in installation space, and also allows the weight and cost to be reduced.

According to the configuration set forth in claim2, an orifice that regulates the amount of oil is provided between the oil pressure chamber and the second oil pressure chamber. By suitably designing the orifice, the flow resistance of the oil flowing between the second oil pressure chamber and the oil pressure chamber can be set to provide an appropriate damping force, which in turn enables a pressing force of the biasing means on the plunger in the advancing direction to be correctly set.

According to the configuration set forth in claim3, the relief valve unit is disposed such as to allow the oil to circulate back to the oil supply part. Since no oil is released to the outside and oil consumption is reduced, the oil pump performance need not be enhanced.

According to the configuration set forth in claim4, a second relief valve unit is further provided, which allows the oil to circulate back to the oil supply part when the pressure of the oil pressure chamber reaches or exceeds a predetermined high level, and the second relief valve unit has a higher valve opening pressure than that of the relief valve unit. This feature enables even higher speed and higher load applications to be covered, for which an excessive load needs to be avoided because the chain tension becomes very high. Thus the applicable operation range can be further extended.

According to the configuration set forth in claim5, the check valve unit is disposed as a valve element of the second relief valve unit, and the second relief valve unit and the check valve unit are formed integral with each other. Therefore, even though the relief valve unit and the check valve unit are assembled inside, they do not cause the tensioner to become bulky.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A chain tensioner100according to a first embodiment of the present invention will be described with reference to the drawings.

The chain tensioner100includes, as shown inFIG. 1, a tensioner body110having a cylindrical plunger bore111with one open end, a cylindrical plunger120slidably inserted in the plunger bore111, and a coil spring140that is biasing means accommodated inside an oil pressure chamber101formed between the plunger bore111and the plunger120such as to be able to expand and contract and to urge the plunger120in an advancing direction.

An oil supply part103, to which oil is supplied from the engine or the like, is formed in the surface of the tensioner body110that is attached to the engine or the like.

In a bottom part112of the plunger bore111is provided a check valve unit150, so that the oil supplied to the oil supply part103is delivered through an oil supply hole114via the check valve unit150into the oil pressure chamber101.

The check valve unit150includes a check ball151, a check valve seat153that opens and closes as the check ball151sits thereon and separates therefrom, a retainer152holding the check ball151inside the check valve seat153, and a ball pressing spring154that lightly presses the check ball151toward the check valve seat153.

The plunger120has a large-diameter part121on one side thereof closer to the bottom part112of the plunger bore111such as to be in sliding contact with a cylindrical surface113of the plunger bore111. A distal end sealing115is provided on the distal end side of the plunger bore111such as to be in contact with part of the plunger120other than the large-diameter part121.

Therefore, between an outer circumferential surface of the plunger120and the cylindrical surface113of the plunger bore111is formed a second oil pressure chamber102, which is defined by the large-diameter part121of the plunger120moving back and forth, and the distal end sealing115, and whose volume increases with a backward movement of the plunger120.

Oil leaks through a gap between the large-diameter part121and the cylindrical surface113and flows between the oil pressure chamber101and the second oil pressure chamber102. An orifice122is provided in the large-diameter part121for regulating the amount of this leaking oil.

The tensioner body110includes a relief valve unit130that releases oil to the oil supply part103when the pressure of the second oil pressure chamber102reaches or exceeds a predetermined high level.

While this embodiment employs the relief valve unit130that has a ball valve, the valve unit may be of any type.

How the chain tensioner100according to the first embodiment of the present invention configured as described above operates will be explained.

Oil is supplied from the oil supply hole114via the check valve unit150into the oil pressure chamber101, and the oil in the oil pressure chamber101is delivered to the second oil pressure chamber102via the orifice122.

At the start of the engine after a long stop, the oil pressure chamber101and second oil pressure chamber102are not filled with oil, so that no damping force acts, as no oil passes through the orifice122.

The spring load of the coil spring140directly acts as the pressing force for the plunger120to advance, and therefore by designing the coil spring140to have a sufficiently large spring load, rattling or looseness of the chain can be prevented.

After the start of the engine, when the engine rpm reaches a normal range, the oil pressure chamber101and second oil pressure chamber102are filled with oil.

During the engine operation, the plunger120stays substantially at the same position, while being biased toward the advancing direction by the spring load of the coil spring140and the hydraulic pressure from the oil pressure chamber101, and reciprocated in accordance with the tension fluctuations of the chain.

Once the plunger120is pushed in, and moves in the advancing direction after that, a flow of oil from the second oil pressure chamber102back into the oil pressure chamber101is generated because of the reduction in volume of the second oil pressure chamber102, whereby a damping force acts as a force in a direction in which the pressing force of the coil spring140on the plunger in the advancing direction is reduced.

Therefore, even though the spring load of the coil spring140is set high so as to prevent rattling or looseness of the chain at the start of the engine, the plunger is prevented from advancing with an unnecessarily large force to push the chain with too much force and to increase the chain tension. Accordingly, the friction properties between the chain and its running surface are improved, and a noise increase or degradation of engine fuel economy are prevented.

When the engine rpm further increases to a high speed range, the load increases, too, and so does the chain tension. The pressure levels of the oil pressure chamber101and of the second oil pressure chamber102rise, too, which causes the relief valve unit130to open.

Therefore, when the plunger120is pushed in and then advances, the oil is released from the second oil pressure chamber102via the relief valve unit130, so that no oil flows back to the oil pressure chamber101, i.e., the hydraulic damping force is no longer generated when the plunger120advances.

Consequently, no force acts in a direction in which the pressing force of the biasing means on the plunger120in the advancing direction is reduced, and the spring load of the coil spring140directly acts as a pressing force for the plunger120to advance, which means that the coil spring140designed to have a large spring load can apply a sufficiently high pressing force to counterbalance the high chain tension.

The relief valve unit130is disposed such as to allow the oil to circulate back to the oil supply part103, so that no oil is released to the outside. Oil consumption is thus reduced, which obviates the need for enhancing the oil pump performance.

The chain tensioner100baccording to the second embodiment of the present invention includes, as shown inFIG. 2, a second relief valve unit160that allows the oil to circulate back to the oil supply part103when the pressure of the oil pressure chamber101reaches or exceeds a predetermined high level. The check valve unit150is disposed as a valve element of the second relief valve unit160, and the second relief valve unit160and the check valve unit150are formed integral with each other.

The second relief valve unit160includes, as shown inFIG. 3A, a relief sleeve161that slidably holds the check valve unit150inside, a relief valve seat162that opens and closes as the check valve unit150slides, and a unit pressing spring163for pressing the check valve unit150toward the relief valve seat162. One end of the unit pressing spring163is seated inside the tensioner body110.

Optionally, a spring retainer that supports and fixes the unit pressing spring163may be fixedly attached to the relief sleeve161.

The relief sleeve161includes, on the rear side of the relief valve seat162, a relief hole165that is a relief part for letting out the oil that is released when the pressure reaches or exceeds a predetermined high level to the outer circumferential side. An orifice167is formed on one side of the relief hole165closer to the oil supply hole114.

The check valve unit150includes a check ball151, a check valve seat153that opens and closes as the check ball151sits thereon and separates therefrom, a retainer152holding the check ball151inside the check valve seat153, and a ball pressing spring154that lightly presses the check ball151toward the check valve seat153.

The check valve seat153has a cylindrical outer shape and is configured to sit on the relief valve seat162of the second relief valve unit160.

The valve opening pressure of the second relief valve unit160is set higher than the valve opening pressure of the relief valve unit130.

Other features are similar to those of the first embodiment and will not be described.

How the chain tensioner100baccording to the second embodiment of the present invention configured as described above operates will be explained.

The operation at the start of the engine after a long stop, and the operation in the normal range and until the rpm reaches the high speed range are the same as those of the first embodiment.

In this embodiment, when the rpm reaches an even higher speed range, and the pressure of the oil pressure chamber101further rises, the second relief valve unit160designed to have a higher valve opening pressure than that of the relief valve unit130opens, so as to reduce the hydraulic pressing force, as well as to lower the damping force when the plunger120is retracted. This way, the plunger can better follow a peak tension, and even higher speed and higher load applications can be covered, for which an excessive load needs to be avoided because the chain tension becomes very high.

The second relief valve unit160is disposed such as to allow the oil to circulate back to the oil supply part103, so that no oil is released to the outside. Oil consumption is thus reduced, which obviates the need for enhancing the oil pump performance.

The characteristics of the pressing force exerted by the chain tensioner according to the present invention are shown inFIG. 4.

With the prior art chain tensioner, the pressing force of the advancing plunger was substantially constant, irrespective of the rpm, corresponding to the spring load of the coil spring that is the biasing means.

With the chain tensioner according to the present invention, at the start (with an rpm at or below point a), the oil pressure chamber101and second oil pressure chamber102are not filled with oil and there is no hydraulic pressure, so that the spring load of the coil spring as the biasing means directly acts as the pressing force.

In the normal range (rpm from point a to b), the oil pressure chamber101and second oil pressure chamber102are filled with oil and, as described above, the presence of the second oil pressure chamber102generates a force that acts to reduce the pressing force on the plunger in the advancing direction, and therefore the pressing force is maintained small.

In the high speed range (rpm at or above point b), as described above, the relief valve unit130opens to negate the effect of the second oil pressure chamber102so that, as with the prior art chain tensioner, the spring load of the coil spring as the biasing means again directly acts as the pressing force.

Moreover, in the second embodiment, in an even higher speed range (rpm at or above point c), the second relief valve unit160opens, so as to reduce the hydraulic pressing force.

The pressing force provided by the oil in the oil pressure chamber101increases with an increase in rotation speed, but since the increase is not a great ratio relative to the spring load of the coil spring that is the biasing means, the pressing force is simply illustrated as constant in the drawing.

The graphs inFIG. 4show exaggerated profiles so that, changes are more easily seen and do not indicate actual values.

While a specific example of the chain tensioner according to the present invention has been described in the embodiments above, the chain tensioner according to the present invention is not limited to these examples, and the shapes, positions, sizes, and positional relationships with each other of various constituent parts may be changed in various manners.

The chain tensioner of the present invention may not necessarily be applied to a chain guide mechanism that uses a guide shoe for slidably guiding a transmission chain such as an endless roller chain passing over respective sprockets of a crankshaft and a cam shaft in an engine room, but may also be adopted in applications where the chain is slidably guided directly by the distal end of the plunger.

The chain tensioner may not necessarily be applied to a chain transmission mechanism but also used for similar transmission mechanisms that use belts, ropes and the like, and can be applied in a variety of industrial fields.