TECHNICAL FIELD

The present invention relates to a tensioning device for producing tension in a chain, and more specifically it relates to an improved structure for increasing the pressing force on a chain as chain elongation increases.

PRIOR ART

A tensioning device having a tensioner arm on which a chain slides, and a hydraulic tensioner which causes a pressing force to act on the tensioner arm in such a way that the tensioner arm is urged toward the chain, is employed as a tensioning device for producing tension in a chain, as shown in Figure 1 of Japanese Unexamined Utility Model Application Publication H6-45141, for example. The hydraulic tensioner consists of a housing, a plunger which is slidably supported inside the housing, a spring for urging the plunger so as to protrude from the housing, and a chamber which is formed between the plunger and the housing, inside the housing.

When slack is produced in the chain during operation, the plunger protrudes toward the chain because of the elastic repelling force of the spring, and oil is introduced into the chamber at this point. Then, when the pressing force on the chain from the plunger caused by the combined force of the hydraulic pressure inside the chamber and the urging force of the spring is balanced with the resistance acting on the plunger from of the chain, the movement of the plunger is stopped. With the conventional tensioning device described above, the amount of elastic deformation of the spring decreases as the spring extends when the plunger is protruding, and therefore the urging force produced by the spring decreases. Accordingly, the pressing force acting on the chain from the plunger decreases when slackness is produced in the chain. With the conventional device described above, it is also necessary to provide a tensioner arm separately to the hydraulic tensioner, which makes the overall device larger. PATENT DOCUMENT 1

Japanese Unexarnined Utility Model Application Publication H6-45141 (see Figure 1)

DISCLOSURE OF THE INVENTION

ISSUE TO BE RESOLVED BY THE INVENTION

The present invention has been devised in view of the conventional situation outlined above, and the issue addressed by the present invention is that of providing a compact tensioning device which makes it possible to increase the pressing force on a chain as chain elongation increases.

MEANS OF RESOLVING THE ISSUE

The inventive tensioning device disclosed in claim 1 is provided with: a tensioner arm having a chain sliding surface on which a chain slides, and having a free end pivotable about a supported end which is supported by a fixed wall, with a hole being formed in the free end; a rotary piston part which is pivotably supported in the hole in the free end, and has an outer peripheral surface which forms first and second chambers with the inner peripheral surface of the hole, the piston part also having a spindle mounting hole which lies offset from the center of the hole; a spindle which is inserted into the spindle mounting hole in the rotary piston part, and which is attached to the fixed wall lying around the tensioner arm; a first oil supply channel which is formed inside the spindle and is supplied with hydraulic pressure from the engine; and a second oil supply channel which is formed in the rotary piston part and is intended for introducing hydraulic pressure supplied to the first oil supply channel into the first chamber. When hydraulic pressure has been introduced into the first chamber, the rotary piston part rotates about the spindle, whereby the free end of the tensioner arm pivots toward the chain about the supported end so that a pressing force acts on the chain.

According to the invention disclosed in claim 1, when slack is produced in the chain during operation, hydraulic pressure is introduced into the first chamber, from the first oil supply channel and through the second oil supply channel. When this happens, the rotary piston part rotates about the spindle. At this point, the spindle mounting hole into which the spindle is inserted is provided offset from the center of the hole in the free end of the tensioner arm (i.e. it is eccentric), and therefore the rotary piston part protrudes toward the chain as the rotary piston part pivots about the spindle, which causes the free end of the tensioner arm to move toward the chain, by way of the hole in the free end of the tensioner arm. As a result, the amount of pushing by the free end of the tensioner arm toward the chain is increased, and a pressing force acts on the chain.

In this case, the pressing force which acts on the chain comes from the hydraulic pressure acting in the chamber rather than from the elastic repelling force of a spring, and as the rotary piston part rotates, the distance between the line of action of the force exerted by the rotary piston part on the hole at the free end of the tensioner arm and the center of the spindle mounting hole becomes steadily shorter (see Figures 2A and 2B). and therefore the force exerted by the rotary piston part on the hole at the free end of the tensioner arm (hence the pressing force acting on the chain) increases as the amount of pushing by the rotary piston part toward the chain increases, accompanying rotation of the rotary piston part, because of the moment balance of the forces around the center of the spindle mounting hole.

Moreover, there is no provision here for a separate hydraulic tensioner in addition to the tensioner arm, so the overall device can be made more compact because it is designed with a hole formed in the free end of the tensioner arm, and a rotary piston part and first and second chambers are provided inside said hole.

In the invention disclosed in claim 2, which is in accordance with claim 1, a check valve is provided between the first oil supply channel and the second oil supply channel, said check valve allowing the flow of oil toward the first chamber, while preventing the flow of oil in the opposite direction. In this case, when hydraulic pressure is introduced into the first chamber, oil is introduced from the first and second oil supply channels via the check valve. Furthermore, if an excessive pressing force from the chain acts on the free end of the tensioner arm, when there is chain resonance for example, the outflow of oil from the first chamber is restricted by the check valve, which prevents a sharp decrease in the volume of the first chamber, making it possible to prevent a sudden retraction of the free end of the tensioner arm. In the invention disclosed in claim 3, which is in accordance with claim 1, ratchet teeth are formed on the inner peripheral surface of the hole in the free end of the tensioner arm, and a pawl which is urged into engagement with the ratchet teeth is provided on the rotary piston part; pivoting of the free end of the tensioner arm is allowed toward the chain, while pivoting away from the chain is restricted by means of the ratchet mechanism which consists of the ratchet teeth and the pawl.

In this case, when slack is produced in the chain and the free end of the tensioner arm moves toward the chain, the ratchet mechanism slips to allow the free end of the tensioner to pivot toward the chain. Furthermore, when the free end of the tensioner arm is pushed by the pressing load from the chain, the ratchet mechanism locks, restricting pivoting of the free end of the tensioner away from the chain, which prevents a sharp decrease in the volume of the first chamber, making it possible to prevent a sudden retraction of the free end of the tensioner arm. In the invention disclosed in claim 4, which is in accordance with claim 1, the supported end of the tensioner arm is slidably supported on the fixed wall which lies around said tensioner arm. Furthermore, in the invention disclosed in claim 5, which is in accordance with claim 1, a long hole is provided in the supported end of the tensioner arm, and a pin which is inserted into the long hole is fixed in the fixed wall.

When the rotary piston part pivots about the spindle, the rotary piston part moves by a certain amount toward the supported end of the tensioner arm or away from the supported end, as a result of which the supported end of the tensioner arm moves by a certain amount, but in this case the supported end is slidably fixed on the fixed w ^r all (invention of claim 4), and the pin which is fixed in the fixed w ^r all is inserted into the long hole in the supported end (invention of claim 5), so this mechanism allows the movement of the supported end of the tensioner arm to be absorbed.

In the invention disclosed in claim 6, which is in accordance with claim 1, the second chamber is open to the atmosphere.

In this case, when hydraulic pressure has been introduced into the first chamber, the volume of the first chamber increases, as a result of which the volume of the second chamber decreases, leading to compression, but at this point. surplus oil produced by the decrease in volume is discharged from the second chamber into the atmosphere.

ADVANTAGES OF THE INVENTION As described above, according to the inventive tensioning device, a hole is formed at the free end of the tensioner arm and a rotary piston part is rotatably provided inside the hole; first and second chambers are also formed, and a spindle mounting hole is formed in the rotary piston part at a position which is offset from the centre of the hole; the spindle is inserted into a spindle insertion hole and attached to the surrounding fixed wall, and first and second oil supply channels are additionally provided in order to introduce hydraulic pressure into the first chamber, and therefore when there is chain elongation the rotary piston part pivots about the spindle while rotating inside the hole at the free end of the tensioner arm, whereby the rotary piston part protrudes toward the chain and the amount of pushing by the free end of the tensioner arm toward the chain is increased.

In this case, the pressing force which acts on the chain comes from the hydraulic pressure acting in the chamber rather than from the elastic repelling force of a spring, and as the rotary piston part rotates, the distance between the line of action of the force exerted by the rotary piston part on the hole at the free end of the tensioner arm and the center of the spindle mounting hole becomes steadily shorter, and therefore the force exerted by the rotary piston part on the hole at the free end of the tensioner arm (hence the pressing force acting on the chain) increases as the amount of pushing by the rotary piston part tow ^r ard the chain increases, accompanying rotation of the rotary piston part. Moreover, there is no provision here for a separate hydraulic tensioner in addition to the tensioner arm, so the overall device can be made more compact because it is designed with a hole formed in the free end of the tensioner arm, and a rotary piston part and first and second chambers aie provided inside said hole.

BEST MODE FOR CARRYING OUT THE INVENTION

Figures 1 to 3 illustrate the tensioning device according to an exemplary embodiment of the present invention, w ^r here Figure 1 is a schematic front view of a timing chain system which employs the tensioning device according to this exemplary embodiment, Figure 2A is an enlarged view of the free end of the tensioner arm in Figure 1. Figure 2 B shows the free end of the tensioner arm of Figure 2A when it has moved toward the chain, and Figure 3 is a view in cross section along the line III-III in Figure 2A. As shown in Figure 1, this timing chain system 100 consists of a crank sprocket 101 which is mounted on an engine crankshaft, cam sprockets 102, 103 which are mounted on a camshaft, and a timing chain 104 which is wound around these sprockets 101 , 102, 103. It should be noted that the arrows in the figures show the direction of rotation of the sprockets. The tensioning device 1 is provided at the slack side span of the timing chain 104. The tensioning device 1 has a tensioner arm 2 comprising a supported end 20 which can slide on a fixed wall 50 such as an engine cylinder block, a free end 21 which can pivot about the supported end 20, and a chain sliding surface 21a which is arranged betw ^r een the supported end 20 and the free end 21 and on w ^r hich the chain 104 slides.

As shown in Figures 2 A and 3, a circular hole 21a is formed at the free end 21 of the tensioner arm 2. A rotary piston part 40 is rotatably supported inside the hole 21a. The rotary piston part 40 has an outer peripheral surface which forms first 22 and second 23 chambers with the inner peripheral surface of the hole 21a. The first 22 and second 23 chambers are separated from each other by two pins 30, 31 which are implanted at the edge of the hole 21a of the tensioner arm 2. The outer peripheral surface of the rotary piston part 40 is always in contact with the outer peripheral surfaces of the pins 30, 31, and when the rotary piston part 40 rotates, the outer peripheral surface thereof slides on the outer peripheral surfaces ofthe pins 30, 31.

The rotary piston part 40 has a bolt insertion hole (spindle mounting hole) 40a at a position which is offset from the center O of the hole 21a (see center Ob). A mounting bolt (spindle) 5 is inserted into the bolt insertion hole 40a. A thread of the mounting bolt 5 is screwed tight into the fixed wall (the cylinder block, for example) 50 which lies around the tensioner arm 2. The rotary piston part 40 can pivot about the mounting bolt 5. A first oil supply channel 5a to which hydraulic pressure from the engine is supplied is formed inside the mounting bolt 5. The first oil supply channel 5a consists of a channel running in the axial direction inside the mounting bolt 5, and a channel running perpendicular thereto. An oil supply channel 40b which communicates with the first oil supply channel 5a is formed in the rotary piston part 40. A second oil supply channel 40c which communicates with the oil supply channel 40b via a check valve 41 is also formed in the rotary piston part 40. The end point of the second oil supply channel 40c opens into the first chamber 22. The check valve 41 consists of a ball and a valve spring which urges this ball toward a valve seat at the lower part of Figure 3, and this valve acts so as to allow the flow of oil to the second oil supply channel 40c from the oil supply channel 40b, whϋe preventing the flow of oil in the opposite direction.

A ratchet mechanism 6 is provided at the free end 21 of the tensioner arm 2. This ratchet mechanism 6 comprises a number of ratchet teeth 60 which are formed on the inner peripheral surface of the hole 21a, and a pawl 61 which is provided on the rotary piston part 40 and which can engage with the ratchet teeth 60. The pawl 61 is provided so as to be able to pivot about a pin 62, and the pawl is urged toward the ratchet teeth 60 by an urging member which is not depicted. The ratchet mechanism 6 is designed so as to allow pivoting of the free end 21 of the tensioner arm 2 toward the chain (clockwise rotation of the rotary piston part 40 in Figure 2A), while pivoting away from the chain is restricted (counterclockwise rotation of the rotary piston part 40 in the same figure).

An end cap 7 is fitted to the end surface of the free end 21 of the tensioner arm 2 (not shown in Figure 2A). The end cap 7 is fixed to the end surface of the free end 21 by means of the mounting bolt 5. The second chamber 23 is open to the atmosphere via a through-hole 6a which is formed in the end cap 7.

The operational effects of this exemplary embodiment will be described next.

As shown in Figures 1 and 2 A, when the timing chain 104 has not yet undergone elongation due to wear, the pressing force which the rotary piston part

40 exerts on the free end 21 of the tensioner arm 2 via the pin 30 by means of the hydraulic pressure supplied to the first chamber 22 is denoted F ₂ , and the distance between the line of action of the pressing force F ₂ and the center Ob of the mounting bolt 5 is denoted L ₂ . Furthermore, if the moment of clockwise rotation in Figure 2A of the rotaty piston part 40 due to the hydraulic pressure acting inside the first chamber 22 is M ₁ , the following equation can be established for the rotary piston part 40 from the moment balance of the forces in relation to the center Ob of the mounting bolt 5: Mi = -FyL ₂

Here, -F ₂ is the reaction force of the pressing force F ₂ , and it acts on the rotary piston part 40 in the opposite direction. Solving this for F ₂ , we obtain: F ₂ = -M ₁ ZL ₂ ...(1).

Next, if the timing chain 104 is elongated due to wear, hydraulic pressure from the engine is supplied to the first chamber 22, via the first oil supply channel 5a, the oil supply channel 40b, the check valve 41 , and the second oil supply channel 40c. When this occurs, the rotary piston part 40 rotates clockwise in Figure 2A about the mounting bolt 5, and the volume of the first chamber 22 increases (see Figure 2B), and the free end 21 of the tensioner arm 2 pivots about the supported end 20. At this point, the rotary piston part 40 protrudes toward the chain (the right-hand side in the Figure), and the amount of pushing by the free end 21 of the tensioner arm 2 toward the chain increases. Furthermore, when the rotary piston part 40 rotates, the ratchet mechanism 6 slips, allowing the rotary piston part 40 to rotate. Moreover, when the free end 21 of the tensioner arm 2 pivots about the supported end 20, the free end 21 moves by a certain amount in the vertical direction in Figure 1. but this movement is absorbed because the supported end 20 slides on the fixed wall 50.

In the state shown in Figure 2B, the pressing force which the rotary piston part 40 exerts on the free end 21 of the tensioner arm 2 via the pin 30 by means of the hydraulic pressure supplied to the first chamber 22 is denoted F ₂ '. and the distance between the line of action of the pressing force F ₂ ' and the center Ob of the mounting bolt 5 is denoted L ₂ '. Furthermore, if the moment of clockwise rotation in Figure 2A of the rotary piston part 40 due to the hydraulic pressure acting inside the first chamber 22 is Mi', the following equation can be established for the rotary piston part 40 from the moment balance of the forces in relation to the center Ob of the mounting bolt 5: M ₁ ' = -F ₂ '-L ₂ '

Here, -F ₂ ' is the reaction force of the pressing force F ₂ ', and it acts on the rotary piston part 40 in the opposite direction. Solving this for F ₂ ', we obtain: F ₂ ^' = -M ₁ ³ ZL ₂ ' = -MiZL ₂ ' [ Y M ₁ = Mr] ...(2).

If we now compare the right-hand sides of equations (1) and (2), we find that L ₂ ' < L ₂ , and therefore F ₂ ' > F ₂ .

In this way, the pressing force exerted on the chain by the free end 21 of the tensioner arm 2 increases as the amount of pushing by the free end 21 of the tensioner arm 2 toward the chain increases, accompanying rotation of the rotary piston part 40. When the chain is operating initially without any wear, the pressing force on the chain need not be large, and if it is in fact excessive, the chain will become worn and the chain sliding surface of the tensioner arm will be worn more quickly.

In this exemplary embodiment, when the chain becomes worn, the pressing force on the chain can be increased by rotation of the rotary piston part so that it protrudes toward the chain, as described above, and therefore when the chain is operating initially without any wear, the hydraulic pressure of the hydraulic tensioner can be reduced to lessen the pressing force on the chain. This means that wear on the chain can be reduced during the initial operation, and the engine fuel consumption can be improved. Moreover, there is no provision here for a separate hydraulic tensioner in addition to the tensioner arm, so the overall device can be made more compact because it is designed with a hole formed in the free end of the tensioner arm, and a rotary piston part and first and second chambers are provided inside said hole.

It should be noted that an example has been presented in this exemplary embodiment in which the supported end 20 of the tensioner arm 2 is slidably supported on the fixed wall 50, but the application of the present invention is not limited by this. Figure 4 is a schematic front view of a tensioning device according to another exemplary embodiment of the present invention; the same reference symbols are used in this figure for components which are the same as, or correspond to, the components of the exemplary embodiment described above.

As shown in Figure 4, a long hole 20a is formed in the supported end 20 of the tensioner arm 2. and the supported end 20 is pivotably supported on the fixed wall, such as the cylinder block, by way of a pin 25 which is inserted into the long hole 20a.

In this instance, the vertical movement of the free end 21 which occurs when the free end 21 of the tensioner arm 2 pivots about the supported end 20 can be absorbed by the long hole 20a.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic front view of a timing chain system which employs the tensioning device according to an exemplary embodiment of the present invention; Figure 2 A is an enlarged view of the free end of the tensioner arm in Figure l;

Figure 2B shows the free end of the tensioner arm (Figure 2A) when it has moved toward the chain;

Figure 3 is a view in cross section along the line III-III in Figure 2A: and Figure 4 is a schematic front view of a tensioning device according to another exemplary embodiment of the present invention.

KEY TO SYMBOLS

1: tensioning device tensioner arm

20: supported end

21a: hole

22: fust chamber

23: second chamber

5: mounting bolt

5a: first oil supply channel

40: rotary piston part

40a: bolt mounting hole

40c: second oil supply channel

50: fixed wall

104: chain

O: center of hole