GB2501294A - A tensioner ratchet seizure release mechanism - Google Patents

Abstract

A ratchet-type tensioner comprises (100, fig 2A) comprises a housing body 110 having a plunger 120 accommodated in a plunger hole (112). The plunger 120 has rack teeth (122) which engage with ratchet teeth (151) on a columnar ratchet element (150) received in a ratchet receiving hole (113). A ratchet release mechanism comprises a tool pin T having a pin edge portion T1 which engages a tool engaging portion 154 provided on the ratchet element (150) when the tool pin T is inserted into an inserting hole 114 in the housing body 110. A tapered abutment surface (254a) may be provided on the ratchet element. If a seizure of the plunger 120 occurs, e.g. due to excessive projection caused by temperature changes, the tool pin T is inserted through hole 114 and a prying force is applied so as to push back the element (150) and release the plunger 120. The ratchet release mechanism reduces a burden of maintenance work such as positioning a replacement of parts.

Description

RATCHET-TYPE TENSIONER

BACKGROUND OF THE INVENTION

Field of the Invention

(0001) The present invention relates to a ratchet-type tensioner for applying tension to a timing chain for driving camshafts and others of an engine.

Related Art (0002) Hitherto, there has been known to use a tensioner for applying tension to a timing chain for driving camshafts and others of an engine by exerting ejection force on a plunger, slidably and fittingly inserted into a housing and forming an oil chamber with the housing, by a spring and external hydraulic pressure.

[0003] As such prior art tensioner, there is adopted a ratchet-type tensioner 500 as shown in FIG. 16 for example.

The ratchet-type tensioner 500 comprises a housing 512, a plunger 514 slidably accommodated in the housing 512, a piston 526 slidably and fittingly inserted into the housing 512 in a direction traverse a sliding direction of the plunger 514 and forming a oil sub-chamber 520 between the housing 512 and the piston 526, an oil passage 544 for exerting external hydraulic pressure to the oil sub-chamber 520, a second spring 534 for biasing the piston 526 toward the oil sub-chamber 520, an air chamber 528 provided on the side opposite from the oil sub-chamber 520, sectioned and formed by the housing 512 and the piston 526 and including the second spring 534, a cap 530 fitted into the air chamber 528, an air communicating hole 532 provided in communication with the air chamber 528 and closed by the piston 526 when the external hydraulic pressure acts on the oil sub-chamber 520 and the piston 526 moves against a biasing force of the second spring 534, rack teeth 538 engraved on a part of the plunger 514 surrounded by the housing 512, and a plurality of engaging teeth 536 provided at an edge of a rod 524 fixed to the piston 526 and capable of engaging with the rack 538, wherein plunger-setback blocking tooth surfaces of the engaging teeth 536 and the rack 538 are formed at right angles with respect to a direction in which the plunger 514 advances/sets back (see Patent Document 1 for example).

PRIOR ART DOCUMENT

PATENT DOCUMENT

[0004) Patent Document 1: Japanese Utility Model No. 2559664 (Claims, FIG. 1) Problems to be Solved by the Invention [0005] However, because the cap 530 is sealed by means of press-fitting in a state in which the rod 524 having the plurality of engaging teeth 536 is accommodated within the air chamber 528, the prior art tensioner 500 as described above has had a problem that such a burden of high-precision work that the cap 530 has to be rigidly and securely assembled is required in assembling the cap 530.

Still more, there has been such a cumbersome problem in terms of maintenance works that the cap 530 cannot be removed and the engagement of the engagement teeth 536 of the rod 524 and the rack 538 of the plunger 514 cannot be released even when the plunger 514 of the ratchet-type tensioner is arbitrarily tried to be pressed and set back in carrying out such maintenance works of positioning the ratchet-type tensioner and the timing chain and of replacing parts by loosening the timing chain.

(00061 Then, because the prior art tensioner 500

described above comprises the columnar plunger 514 and piston 526, it has such problems that it causes an excessive turn-stopping condition in the engagement between the rack 538 of the plunger 514 and the engagement teeth 536 of the piston 526 as the plunger 514 vibrates in driving the engine, thus the engagement teeth 536 of the piston 526 being liable to cause chipping. It also causes a twist across the whole tooth widthwise range, a mismatch of the engagement and an erroneous operation of the ratchet mechanism composed of the engagement teeth 536 and the rack 538 in the end. Stilimore, the prior art tensioner has such a cumbersome problem that the plunger 514 and the piston 526 turn respectively around their axes and cause erroneous assembly with each other during manufacturing and maintaining the tensioner.

(0007] still more, because the plunger setback blocking tooth surfaces of the engagement teeth 536 and the rack 538 are traverse the advance/setback direction of the plunger 514 in the prior art tensioner 500 described above, they restrict also moves of the plunger 514 in the setback direction caused by excessive tension of the chain caused by temperature change and others of the engine. Accordingly, the prior art tensioner 500 has had such problems that the plunger 514 causes seizure or the chain travels with the excessive tension, thus increasing a burden to the chain and noises.

(0008] Due to that, although a predetermined backlash amount is provided in the ratchet mechanism composed of the engagement teeth 536 and the rack 538 corresponding to a presumed maximum value of the move of the plunger 514 in the setback direction caused by the excessive tension, there has been a problem that the larger the backlash amount, the less a rattle noise called a flapping noise generated in starting engine can be reduced.

(0009] Still more, although it is possible to take such measures of adding an orifice mechanism and an oil-reserve mechanism or of replacing the spring 518 with a high-load accommodated spring in order to solve such problem of the rattle noise prone to be generated on starting the engine, there have been such problems that not only a number of parts and production cost therefor increase, but also the tensioner itself is enlarged.

SUMMARY OF THE INVENTION

(0010] Accordingly, the present invention aims at solving the aforementioned prior art problems by providing a ratchet-type tensioner that permits to readily release an engagement of a ratchet mechanism composed of a plunger and a ratchet element in maintaining the ratchet-type tensioner, to securely and stably operate the ratchet mechanism without erroneous operation in operating an engine, to reduce flapping noise by suppressing backlash to a reaction force of the plunger receiving from a timing chain on starting the engine after leaving it for a long period of time and to prevent seizure of the plunger by allowing the plunger to move in a setback direction that is caused by excessive tension of the chain after starting the engine.

Means for Solving the Problems [00111 In order to solve the aforementioned problems, according to a first aspect of the invention, there is provided a ratchet-type tensioner comprising a housing body in which an oil passage for supplying external pressure oil is formed, a plunger-accommodating hole formed in the housing body, a plunger slidably projecting out of the plunger-accommodating hole toward a traveling chain, a high-pressure oil chamber formed between the plunger-accommodating hole of the housing body and a hollow portion of the plunger, a plunger biasing spring stored in the high-pressure oil chamber to bias the plunger in a plunger projection direction, a ratchet-receiving hole formed within the housing, a columnar ratchet element fittingly inserted into the ratchet-receiving hole and sliding in a direction traverse an advance/setback direction of the plunger, rack teeth provided on a side surface of the plunger, ratchet teeth provided at a plunger-side front-end area of the ratchet element, a ratchet biasing spring for biasing the ratchet element so that the ratchet teeth engage with the rack teeth, a spring stopping plug fitted into a rear-end area of the ratchet-receiving hole to seat the ratchet biasing spring, and a ratchet releasing mechanism for releasing an engagement of the ratchet teeth of the ratchet element to the rack teeth of the plunger, wherein the ratchet releasing mechanism comprises a tool pin engaging portion provided at the plunger-side front-end area of the ratchet element to abut and engage with a pin edge portion of a tool pin and a pin inserting hole provided in the housing body to insert the tool pin toward the tool pin engaging portion.

(0012] According to a second aspect of the invention, the tool pin engaging portion of the ratchet element comprises a stepped abutment surface formed between the ratchet teeth and the outer circumferential surface of the ratchet element at the plunger-side frontend area of the ratchet element, and the pin inserting hole of the housing body is provided so as to push back the ratchet element in a direction opposite from the ratchet element biasing direction by prying the stepped abutment surface of the ratchet element by the tool pin.

[0013] According to a third aspect of the invention, the tool pin engaging portion of the ratchet element comprises a tapered abutment surface formed by partly cutting away the plunger-side frontend area of the ratchet element toward the rear-end area; and the pin inserting hole of the housing body is provided so as to push back the ratchet element in a dir ection opposite from the ratchet element biasing direction by pressing the tapered abutment surface of the ratchet element by the tool pin.

[0014] ccording to a fourth aspect of the invention, the biasing force of the ratchet biasing spring is set to be greater than a component force in the sliding direction of the ratchet element caused by the reaction force that is generated from the traveling chain side and sets back the plunger on starting the engine to be smaller than a component force in the sliding directicn of the ratchet element caused by the reaction force that is generated from the traveling chain side and sets back the plunger when tension of the chain is excessive after starting the engine.

[0015] According to a fifth aspect of the invention, the rack teeth of the plunger are formed concave-convexly respectively by the stop surfaces inclined toward the plunger-advancing side with respect to the sliding direction of the ratchet element and the sliding surfaces inclined toward the plunger-setback side with respect to the sliding direction of the ratchet element, and the ratchet teeth of the ratchet element are formed concavo-convexly respectively by the stop counterface surfaces inclined toward the advance-direction side with respect to the sliding direction of the ratchet element and the sliding counterface surfaces inclined toward the plunger-setback side with respect to the sliding direction of the ratchet.

(0016] According to a sixth aspect of the invention, the inclination angle of the stop surface is set to be smaller than the inclination angle of the sliding surface.

(0017] According to a seventh aspect of the invention, an engagement matching mechanism that engages the ratchet teeth of the ratchet element to the rack teeth on the side surface of the plunger without twisting a whole widthwise range of the teeth is constructed so as to stop an outer circumferential surface of the ratchet element from turning against an inner circumferential surface of the cylindrical ratchet-accommodating hole.

(0018) According to an eighth aspect of the invention, the engagement matching mechanism is constructed by a ratchet-side convex strip provided along the sliding direction on the outer circumferential surface of the ratchet element and a housing-side concave groove provided along the sliding direction on the inner circumferential surface of the ratchet-accommodating hole in a condition of being concavo-convexly engaged with the ratchet-side convex strip.

[0019] According to a ninth aspect of the invention, the ratchet element has a whole length which is greater than an outer diameter thereof.

[0020] According to a tenth aspect of the invention, the ratchet biasing spring is inserted into the spring-accommodating hole of* the ratchet element along the sliding direction.

[Advantageous Effects of the Invention] [0021] Then, because the ratchet-type tensioner of the inventioncomprises thehousingbodyinwhichtheoilpassage for supplying external pressure oil is formed, the plunger-accommodating hole formed in the housing body, the plunger slidably projecting out of the plunger-accommodating hole toward the traveling chain, the high-pressure oil chamber formed between the plunger-accommodating hole of the housing body and the hollow portion of the plunger, the plunger biasing spring stored in the high-pressure oil chamber to bias the plunger in the plunger projection direction, the ratchet-receiving hole formed within the housing, the columnar ratchet element fittingly inserted into the ratchet-receiving hole and sliding in the direction traverse the advance/setback direction of the plunger, the rack teeth provided on the side surface of the plunger, the ratchet teeth provided at the plunger-side front-end area of the ratchet element, the ratchet biasing spring for biasing the ratchet element so that the ratchet teeth engage with the rack teeth, and the spring stopping plug fitted into a rear-end area of the ratchet-receiving hole to seat the ratchet biasing spring, it is possible not only to apply tension to a timing chain within an engine from the plunger of the ratchet-type tensioner but also to bring about the following advantageous effects peculiar to the invention.

(0022] That is, according to the ratchet-type tensioner of the first aspect of the invention, because the ratchet releasing mechanism for releasing the engagement of the ratchet teeth of the ratchet element to the rack teeth of the plunger comprises the tool pin engaging portion provided at the plunger-side front-end area of the ratchet element to abut and engage with the pin edge portion of the tool pin and the pin inserting hole provided in the housing body to insert the tool pin toward the tool pin engaging portion, it is possible to push and set back the plunger of the ratchet-type tensioner by readily releasing the engagement of the ratchet teeth of the ratchet element to the rack teeth of the plunger by abutting and engaging the pin edge portion of the tool pin to the tool pin engaging portion of the ratchet element through the pin inserting hole, so that it is possible to considerably reduce a burden of maintenance works such as positioning and replacement of parts of the ratchet-type tensioner and the timing chain in a condition in which the timing chain is loosened.

[0023] According to the ratchet-type tensioner of the second aspect of the invention, because the tool pin engaging portion of the ratchet element comprises a stepped abutment surface formed between the ratchet teeth and the outer circumferential surface of the ratchet element at the plunger-side frontend area of the ratchet element, and the pin inserting hole of the housing body is provided so as to push back the ratchet element in a direction opposite from the ratchet element biasing direction by prying the stepped abutment surface of the ratchet element by the tool pin, a prying force of the tool pin inserted through the pin inserting hole of the housing body acts on the stepped abutment surface so as to push back the ratchet element in the direction opposite from the ratchet element biasing direction. Therefore, it is possible to readily release the engagement of the ratchet teeth of the ratchet element to the rack teeth of the plunger.

[0024] According to the ratchet-type tensioner of the third aspect of the invention, because the tool pin engaging portion of the ratchet element comprises a tapered abutment surface formed by partly cutting away the plunger-side frontend area of the ratchet element toward the rear-end area and the pin inserting hole of the housing body is provided so as to push back the ratchet element in a direction opposite from the ratchet element biasing direction by pressing the tapered abutment surface of the ratchet element by the tool pin, a pressing force of the tool pin inserted through the pin inserting hole of the housing body generates a component force that acts on the tapered abutment surface so as to push back the ratchet element in the direction opposite from the ratchet element biasing direction. Therefore, it is possible to readily release the engagement of the ratchet teeth of the ratchet element to the rack teeth of the plunger.

(0025] According to the ratchet-type tensioner of the fourth aspect of the invention, because the biasing force of the ratchet biasing spring is set to be greater than the component force in the sliding direction of the ratchet element caused by the reaction force that is generated from the traveling chain side and sets back the plunger on starting the engine, the ball biasing spring of the ratchet biasing spring acts on the ratchet teeth so as to engage with the rack teeth of the plunger when the reaction force that sets back the plunger is generated on starting the engine.

Therefore, it becomes possible not only to block the setback displacement of the plunger by restricting the move thereof in the setback direction and to reduce the flapping noise of the timing chain but also to reduce the number of parts and the production cost and to downsize the tensioner itself without requiring any special high-load accommodating plunger biasing spring, orifice mechanism and oil reserving mechanism because the ball biasing spring of the plunger biasing spring is sufficient by the biasing force that just biases and projects the plunger.

(00261 Still more, because the biasing force of the ratchet biasing spring is set to be smaller than the component force in the sliding direction of the ratchet element caused by the reaction force that is generated from the traveling chain side and sets back the plunger when tension of the chain is excessive after starting the engine, the biasing force of the ratchet biasing spring acts on the ratchet teeth of the ratchet element, the ratchet teeth of the ratchet element disengage from the rack teeth of the plunger and the plunger is set back until when the biasing force of the ratchet biasing spring becomes relatively greater than the component force in the sliding direction of the ratchet element when the reaction force that sets back the plunger is generated when the tension of the chain is excessive after starting the engine.

Therefore, even if the plunger advances excessively due to temperature change of the engine and others, it becomes possible not only to prevent the seizure of the plunger by allowing the setback displacement by not restricting the move of the plunger in the setback direction, but also to securely prevent the seizure of the plunger because it becomes possible to control the timing of the disengagement caused by the excessive tension of the chain after starting the engine by regulating the biasing force of the ratchet biasing spring.

(0027] According to the ratchet-type tensioner of the fifth aspect of the invention, because the rack teeth of the plunger are formed concave-convexly respectively by the stop surfaces inclined toward the plunger-advancing side with respect to the sliding direction of the ratchet element and the sliding surfaces inclined toward the plunger-setback side with respect to the sliding direction of the ratchet element, and the ratchet teeth of the ratchet element are formed concavo-convexly respectively by the stop counterface surfaces inclined toward the advance-direction side with respect to the sliding direction of the ratchet element and the sliding counterface surfaces inclined toward the plunger-setback side with respect to the sliding direction of the ratchet element, when the reaction force that sets back the plunger is generated when the tension is excessive after starting the engine, the reaction force acts on the stop counterface surfaces of the ratchet element as the component force through the stop surfaces on the plunder side. This component force that acts on the stop counterface surfaces of the ratchet element acts further as the smaller component force in the sliding direction of the ratchet element so as to disengage the ratchet teeth of the ratchet element from the rack teeth of the plunger.

Then, the rack teeth of the plunger slide the sliding counterface surface by going over the stop counterface surface and return by one tooth, so that it becomes possible to smoothly allow the setback displacement without restricting the move of the plunger in the setback direction while preventing wear and damage such as chipping of the teeth that is prone to occur in the ratchet teeth and the rack teeth when the tension of the chain is excessive after starting the engine and to exhibit excellent durability by avoiding excessive impact on the ratchet biasing spring.

(0028] According to the ratchet-type tensioner of the sixth aspect of the invention, because the inclination angle of the stop surface is set to be smaller than the inclination angle of the sliding surface, it becomes possible to block the disengagement of the rack teeth of the plunger and the ratchet teeth of the ratchet element even when the reaction force that sets back the plunger is generated on starting the engine. Therefore, it is possible to block the setback displacement of the plunger by restricting the move in the setback direction thereof causing backlash on starting the engine.

(0029] According to the ratchet-type tensioner of the seventh aspect of the invention, because the engagement matching mechanism that engages the ratchet teeth of the ratchet element to the rack teeth on the side surface of the plunger without twisting the whole widthwise range of the teeth is constructed so as to stop the outer circumferential surface of the ratchet element from turning against the inner circumferential surface of the cylindrical ratchet-accommodating hole, the engagement matching mechanism stops the outer circumferential surface of the ratchet element from turning against the inner circumferential surface of the ratchet-accommodating hole regardless of the engagement between the rack teeth on the side of the plunger and the ratchet element of the ratchet element even when the plunger vibrates during when the engine is driven. Therefore, it is possible to securely and stably operate the ratchet mechanism comprising the plunger and the ratchet element.

Still more, because it is possible to engage the ratchet teeth of the ratchet element to the rack teeth on the side of the plunger precisely across an entire widthwise range, it is possible to eliminate erroneous operation of the ratchet mechanism by avoiding a twist otherwise caused by erroneous assembly between the rack teeth on the side of the plunger and the ratchet teeth of the ratchet element.

[0030] According to the ratchet-type tensioner of the eighth aspect of the invention, because the engagement matching mechanism is constructed by the ratchet-side convex strip provided along the sliding direction on the outer circumferential surface of the ratchet element and the housing-side concave groove provided along the sliding direction on the inner circumferential surface of the ratchet-accommodating hole in the condition of being concavo-convexly engaged with the ratchet-side convex strip, it is possible to slide the ratchet element while completely stopping the outer circumferential surface thereof from turning against the inner circumferential surface of the ratchet-accommodating hole.

Therefore, it is possible to operate the ratchet mechanism comprising the plunger and the ratchet element smoothly and to considerably reduce the burden for producing the engagement matching mechanism, as compared to an engagement matching mechanism provided with a convex strip in the housing-side ratchet-accommodating hole, because the concave groove is provided in the housing-side ratchet-accommodating hole.

(0031] According to the ratchet-type tensioner of the ninth aspect of the invention, because the ratchet element has the whole length which is greater than the outer diameter thereof, it becomes possible to operate the ratchet mechanism comprising the plunger and the ratchet element more smoothly by suppressing inclination and preventing biased wear of the ratchet element, that is otherwise prone to be caused within the ratchet-receiving hole in the sliding direction, even when an overload is applied to the ratchet element.

[0032] According to the ratchet-type tensioner of the tenth aspect of the invention, because the ratchet biasing spring is inserted into the spring-accommodating hole of the ratchet element along the sliding direction, the ratchet biasing spring is inserted substantially within the spring-accommodating hole of the ratchet element.

Therefore, as compared to a case of fitting the ratchet biasing spring around an outer circumferential surface of the ratchet element, it is possible to simplify and downsize the attachment of the ratchet element to the ratchet accommodating hole.

BRIEF DESCRIPTION OF DRAWINGS

(0033] FIG. 1 illustrates a mode of use of a ratchet-type tensioner 100 of a first embodiment of the invention; FIGs. 2A and 2B are enlarged views of a main part of the ratchet-type tensioner shown in FIG. 1; FIG. 3 is an enlarged view of rack teeth and ratchet teeth; FIG. 4 is a section view taken along a line A-A in FIG. 2B; FIG. 5 is an exploded view of a ratchet element, a ratchet biasing spring and a spring stopping plug; FIG. 6 is a diagram illustrating an engagement state of the rack teeth and ratchet teeth associated with a plunger ejecting operation in starting an engine; FIG. 7 is a diagram illustrating an engagement state of the rack teeth and ratchet teeth associated with a plunger setback operation in starting the engine; FIG. B is a diagram iliustratirig an engage*-ent state of the rack teeth and ratchet teeth when the plunger starts to set back when a tension of a chain is excessive; FIG. 9 is a diagram illustrating a disengagement state of the rack teeth and ratchet teeth during the plunger setback operation when the tension of the chain is excessive; FIG. 10 is a diagram illustrating an engagement state of the rack teeth and ratchet teeth when the plunger finishes to set back when the tension of the chain is excessive; FIGs. hA and llB are diagrams explaining a ratchet releasing operation in the first embodiment of the invention; FIGs. l2A and 12B are enlarged views of a main part of a ratchet-type tensioner 200 of a second embodiment of the invention; FIG. 13 is a section view taken along a line B-B in FIG. 126; FIG. 14 is an exploded view of a ratchet element, a ratchet biasing spring and a spring stopping plug; FIGs. iSA and 15B are diagrams explaining a ratchet releasing operation in the second embodiment of the invention; and FIG. 16 is a section view of a prior art ratchet-type tensioner.

PREFERRED EMBODIMENT OF THE INVENTION

(First Embodiment) (0034] One embodiment of the ratchet-type tensioner 100 of the invention will be explained with reference to FIGs.

1 through 15.

Here, FIG. 1 illustrates a mode of use of a ratchet-type tensioner 100 of a first embodiment of the invention, FIGs.

2A and 2B are enlarged views of a main part of the ratchet-type tensioner shown in FIG. 1, FIG. 3 is an enlarged view of rack teeth and ratchet teeth, FIG. 4 is a section view taken along a line A-A in FIG. 2B, FIG. 5 is an exploded view of a ratchet element, a ratchet biasing spring and a spring stopping plug, FIG. 6 is a diagram illustrating an engagement state of the rack teeth and ratchet teeth associated with a plunger ejecting operation in starting an engine, FIG. 7 is a diagram illustrating an engagement state of the rack teeth and ratchet teeth associated with a plunger setback operation in starting the engine, FIG. 8 is a diagram illustrating an engagement state of the rack teeth and ratchet teeth when the plunger starts to set back when a tension of a chain is w excessive, FIG. 9 is a diagram illustrating a disengagement state of the rack teeth and ratchet teeth during the plunger setback operation when the tension of the chain is excessive, FIG. 10 Is a diagram illustrating an engagement state of the rack teeth and ratchet teeth when the plunger finishes to set back when the tension of the chain is excessive and FIGs.

hA and 11B are diagrams explaining a ratchet releasing operation in the first embodiment of the invention.

(0035] As shown in FIG. 1, the ratchet-type tensioner 100 of the first embodiment of the invention is attached to an engine body on a slack side of a timing chain C which is wrapped around a driving sprocket 51 rotated by a crankshaft of the engine and a pair of driven sprockets S2 fixed to camshafts. The ratchet-type tensioner 100 has a housing body 110 and a plunger 120 that slidably projects out of a front surface of the housing body 110. The plunger 120 applies tension to the slack side of the timing chain C through an intermediary of a movable lever L rockably supported on the engine body side by pressing a back of the movable lever L near a rocking end.

It is noted that a stationary guide G for guiding travel of the timing chain C is mounted to the engine body on a tension side of the timing chain C. [0036] When the driving sprocket Si rotates in a direction of an arrow in FIG. 1, the timing chain C travels in the direction of the arrow. Then, the driven sprockets 52 also rotate in the direction of the arrows and thus the rotation of the sprocket Si is transmitted to the driven sprockets 32.

(0037] As shown in FIG. 2, the ratchet-type tensioner has the housing body 110 having an oil supplying path ill for introducing external pressure oil supplied from the engine body side, a plunger-accommcdating hole 112 formed in the housing body 110 to accommodate the plunger 120, the columnar plunger 120 that slidably projects out of the plunger-accommodating hole 112 toward the traveling chain (not shown), a high-pressure oil chamber R formed between the plunger-accommodating hole 112 of the housing body 110 anda hollow portion 121 of the plunger 120, a plunger biasing spring 130 accommodated within the high-pressure oil chamber R and biasing the plunger 120 in the plunger projecting direction, a check valve unit 140 assembled at a bottom portion of the plunger-accommodating hole 112 to block the pressure oil from flowing backward from the high-pressure oil chamber R to the oil supplying path iii, a cylindrical ratchet-receiving hole 113 formed in the housing body 110, a columnar ratchet element 150 fittingly inserted into the ratchet-receiving hole 113 and slides in a direction traverse the advance/setback direction of the plunger 120, a ratchet biasing spring 160 for biasing the ratchet element so that ratchet teeth 151 provided at a plunger-side edge area of the ratchet element 150 engage with rack teeth 122 engraved on a side surface of the plunger and a spring stopping plug 170 fitted into a rear edge area of the ratchet-receiving hole 113 to stop and seat the ratchet biasing spring 160.

(Specific Unit Structure of Check Valve Unit 140) (0038] A specific unit structure of the check valve unit described above may be any known type as long as it is assembled at the bottom portion of the plunger-accommodating hole 112 and blocks the pressure oil from flowing backward from the high-pressure oil chamber R to the oil supplying path 111. However, the present embodiment adopts the check valve unit 140 having a ball seat 141 having an oil passage 142a linked with the oil supplying path 111 of the housing body 110 described above, a check ball 142 seated on a valve seat 141b of the ball seat 141, a ball biasing spring 143 for pressing and biasing the check ball 142 to the ball seat 141 and a bell-like retainer 144 for supporting the ball biasing spring 143 and restricting a move of the check ball 142.

(Specific Structure of Engagement Matching Mechanism) (0039] The ratchet-type tensioner 100 of the present embodiment is provided with an engagement matching mechanism for engaging the ratchet teeth 151 of the ratchet element to the rack teeth 122 on the side surface of the plunger without twisting a whole widthwise range of the teeth.

[0040] That is, as shown in FIGs. 2 and 4, the engagement matching mechanism described above is constructed so as to stop an outer circumferential surface of the ratchet element from turning against an inner circumferential surface of the cylindrical ratchet-accommodating hole 113 provided in a direction orthogonal to the sliding direction of the plunger 120.

This arrangement stops the outer circumferential surface of the ratchet element 150 from turning against the inner circumferential surface of the ratchet-accommodating hole 113 and engages the ratchet teeth 151 of the ratchet element 150 to the rack teeth 122 on the side of the plunger precisely across an entire widthwise range, regardless of the engagement between the rack teeth 122 on the side of the plunger 120 and the ratchet element 150 of the ratchet element 150 even when the plunger 120 vibrates during when the engine is driven.

(00411 More specifically, the engagement matching mechanism described above is constructed by a ratchet-side convex strip 152 having an involute spline section provided along the sliding direction on the outer circumferential surface of the ratchet element 150 and a housing-side concave groove 113a having an involute spline groove provided along the sliding direction on the inner circumferential surface of the ratchet-accommodating hole 113 in a condition of being concavo-convexly engaged with the ratchet-side convex strip w 152.

This arrangement permits the ratchet element 150 to slide while completely stopping the outer circumferential surface thereof from turning against the inner circumferential surface of the ratchet-accommodating hole 113 and considerably reduces a burden for producing the engagement matching mechanism.

[00421 As shown in FIG. 5, the ratchet element 150 described above has a whole length W which is greater than an outer diameter D thereof. This arrangement permits the ratchet mechanism comprising the plunger 120 and the ratchet element 150 to operate more smoothly by suppressing inclination and preventing biased wear of the ratchet element 150, that are otherwise prone to be caused within the ratchet-receiving hole 113 in the sliding direction, even when an overload is applied to the ratchet element 150.

Further, in order to engage with the rack teeth 122 engraved on the side surface of the plunger 120 by homogeneously dispersing the engagement load, the ratchet element 150 of the present embodiment is provided with the three ratchet teeth 151 having teeth intervals equal with pitches of the rack teeth 122 and the same tooth height with the rack teeth 122 at the edge area on the plunger side thereof as shown in FIGs. 3 and 5.

(0043) The ratchet biasing spring 160 described above is inserted concentrically within the ratchet element 150 along the sliding direction as shown in FIG. 5. with this arrangement, the ratchet biasing spring 160 is substantially inserted into a spring-accommodating hole 153 of the ratchet element 150 and as compared with a case of outwardly fitting the ratchet biasing spring 160 around an outer circumferential surface of the ratchet element 150, a configuration for mounting the ratchet element 150 within the ratchet-receiving hole 113 is simplified and downsized.

(0044] Then, the biasing force of the ratchet biasing spring 160 is set to be greater than a component force in the sliding direction of the ratchet element 150 caused by the reaction force that is generated from the traveling chain side on starting the engine and sets back the plunger 120 arid to be smaller than a component force in the sliding direction of the ratchet element 150 caused by the reaction force that is generated from the traveling chain side and sets back the plunger 120 when tension of the chain is excessive after starting the engine.

With this arrangement, it becomes possible to reduce flapping noise of the timing chain by suppressing the setback displacement of the plunger 120 on starting the engine and also to prevent seizure of the plunger 120 by allowing the setback displacement of the plunger 120 when the tension of the timing chain is excessive after starting the engine.

Th±s arrangement also requires no special high-load accommodating plunger biasing spring 160, orifice mechanism w and oil-reserving mechanism, so that it becomes possible to downsize the tensioner itself by reducing a number of parts and production costs.

[0045] The spring stopping plug 170 described above is a so-called stopping washer having, around which, a large number of projecting tongues 171 that exhibit resilience for fitting near a rear edge of the ratchet-accommodating hole 113 and stopping the ratchet element as shown in FIG. 2. The spring stopping plug 170 seats a rear edge of the ratchet biasing spring 160 as shown in FIGs. 2 and 5.

[0046] The mutual relationship of the rack teeth 122 of the plunger 120, the ratchet teeth 151 and the ratchet biasing spring 160 of the ratchet-type tensioner 100 of the present embodiment will be detailed further with reference to FIGs. 3 and 6 through 8.

Firstly, as shown in FIG. 6, when the plunger 120 projects on starting the engine and during normal operation after starting the engine, a relationship of component and biasing forces always turns out as fl > Fs and the plunger advances while pushing back the ratchet element 150.

Here, the biasing force Fs of the ratchet biasing spring 160 used in the present embodiment is set to be greater than the component force fi in the sliding direction of the ratchet element 150 caused by a reaction force Fl that acts from the traveling chain side and sets back the plunger 120 on starting the engine as shown in FIG. 7 and to be smaller e than a component force f2 in the sliding direction of the ratchet element 130 caused by a reaction force F2 that acts from the traveling chain side and sets back the plunger 120 when the tension of the chain is excessive after starting the engine as shown in FIG. 8.

[0047] Due to that, the relationship always turns out as fi > PS when the plunger 120 projects on starting the engine as shown in FIG. 6 and advances following a lever (not shown).

Then, when the first reaction force Ft that tries to set back the plunger 120 is generated from the traveling chain side on starting the engine as shown in FIG. 7, the biasing force Fs of the ratchet biasing spring 160 which is greater than the component force ft in the sliding direction of the ratchet element 150 described above acts on the ratchet teeth 151 of the ratchet element 150. Then, the ratchet teeth 151 engage with the rack teeth 122 of the plunger 120, restrict the move in the setback direction of the plunger 120 causing backlash and block a setback displacement of the plunger 120.

Further, when a reaction force F2 that sets back the plunger 120 is generated from the traveling chain side when the tension of the chain is excessive after starting the engine as shown in FIG. 8, the component force f2 in the sliding direction of the ratchet element 150 described above becomes greater than the biasing force Fs of the ratchet biasing spring 160. Then, the ratchet teeth 151 of the ratchet element 150 disengage from the rack teeth 122 of the w plunger 120 as shown in FIG. 9. Thus, the plunger 120 sets back by one tooth or several teeth of the rack teeth 122 until when the reaction force Fs of the ratchet biasing spring 160 becomes relatively greater than the component force f 2.

Thus, the ratchet-type tensioner 100 is arranged so as not to restrict the move in the setback direction of the plunger causing the backlash due to the excessive tension of the chain after starting the engine and to allow the setback displacement of the plunger 120 as shown in FIG. 10.

[0048] Accordingly, a biasing force of the plunger biasing spring 130 suffices if it is greater than biasing force Fs of the ratchet biasing spring 160 and biases and projects the plunger 120. It is then possible to control the disengagement timing caused by the excessive tension of the chain after starting the engine by adjusting the biasing force Fs of the ratchet biasing spring 160 within such range.

(0049] More specifically, in the ratchet-type tensioner 100 of the present embodiment, the rack teeth 122 of the plunger 120 are formed concavo-convexly by stop surfaces 122a inclined toward the plunger-advance side with respect to the sliding direction of the ratchet element 150 and sliding surfaces 122b inclined toward the plunger-setback side with respect to the sliding direction of the ratchet element 150 as shown in FIG. 3.

The ratchet teeth 151 are formed concavo-convexly by stop counterface surfaces lSla inclined toward the plunger-advance side with respect to the sliding direction of the ratchet element 150 and sliding counterface surfaces l5].b inclined toward the plunger-setback side with respect to the sliding direction of the ratchet element 150.

[0050] With this arrangement, when the reaction force F2 that sets back the plunger 120 is generated from the traveling chain side when the tension of the chain is excessive after starting the engine as shown in FIG. 8, the reaction force F2 acts on the stop counterface surface 151a of the ratchet element 150 as a component force fh through the stop surface 122a of the plunger side. The component force fh that acts on the stop counterface surface iSla of the ratchet element 150 acts as the further smaller component force f2 in the sliding direction of the ratchet element 150 so that the ratchet teeth 151 of the ratchet element 150 disengage from the rack teeth 122 of the plunger 120. Then, as shown in FIGs. 9 and 10, the rack teeth 122 of the plunger slide over the sliding counterface surface 151b by going over the stop counterface surface lSla of the ratchet element and return by one tooth or several teeth.

[0051] Then, an inclination angle 0 of the stop surface 122a formed on the plunger 120 described above is set to be smaller than an inclination angle a of the sliding surface 122b.

This arrangement blocks the rack teeth 122 of the plunger 120 from disengaging from the ratchet teeth 151 of the ratchet element 150 even when the reaction force Fl that sets back the plunger 120 is generated from the traveling chain side on starting the engine.

[0052] Therefore, even when the plunger 120 advances excessively due to temperature change of the engine and others and an overload is generated by backstop as described above, a relationship of magnitudes of the second component force f2 in the sliding direction of the ratchet element 150 caused by the reaction force F2 that is generated from the traveling chain side and sets back the plunger 120 when the tension of the chain is excessive after starting the engine as shown in FIG. 9 and the biasing force Es of the ratchet biasing spring 160 turns out as follows: f2 = F2 x cosO x sine x f2 > Fs Note that j.x here is a coefficient of friction between the rack teeth 122 of the plunger 120 and the ratchet teeth 151 of the ratchet element 150.

[0053] When the move in the setback direction of the plunger 120 causing the backlash is restricted to block the setback displacement on starting the engine as described above, a relationship of magnitudes of the componenL force fl in the sliding direction of the ratchet element 150 caused by the reaction force El that is generated from the traveling chain side and sets back the plunger 120 on starting the engine as shown in FIG. 7 and the biasing force Es of the ratchet biasing spring 160 turns out as follows: fl = El x cosO x sinG x fl < Es Note that! here is the coefficient of friction between the rack teeth 122 of the plunger 120 and the ratchet teeth 151 of the ratchet element 150.

[0054] Next, disengagement operations cf the rack teeth 122 of the plunger 120 and the ratchet teeth 151 of the ratchet element 150 when the tension of the chain is excessive after starting the engine, which is the most characteristic part of the ratchet-type tensioner 100 of the present embodiment, will be explained with reference to FTGs. 8 through 10.

It is noted that imaginary lines shown at the plunger-frontend side in FIGs. 8 and 10 indicate states when the tension of the chain is excessive after starting the engine, i.e., a frontend position of the plunger 120 in the state shown in FIG. 8. still more, imaginary lines near the ratchet element in FIGs. 9 and 10 indicate states when the tension of the chain is excessive after starting the engine, i.e., position of the ratchet element 150 in the state shown in FIG. 8.

[0055] when the reaction force F2 that sets back the plunger 120 is generated from the traveling chain when the tension of the chain is excessive after starting the engine, this reaction force F2 acts on the stop counterface surface 151a of the ratchet element 150 through the stop surface 122a w on the plunger side as the component force fh as shown in FIG. 8. The component force fh acting on the stop counterface surface l5la of the ratchet element 150 acts also as a smaller component force f2 in the sliding direction of the ratchet element 150.

[0056) When the component force f2 in the sliding direction of the ratchet element 150 described above acts, the plunger 120 starts to set back as the stop surfaces 122a on the plunger side slide over the stop counterface surfaces l5la of the ratchet element side as shown in FIG. 9. Thus, the rack teeth 122 of the plunger 120 disengage from the ratchet teeth 151 of the ratchet element 150.

[0057] Next, at the same time when the rack teeth 122 of the plunger 120 disengage from the ratchet teeth 151 of the ratchet element 150, the sliding surfaces 122b on the plunger side start to slide over the sliding counterface surface 151b on the ratchet element side and the plunger 120 continues to set back.

[0058] When the plunger 120 continues to set back further as the sliding surface 122b on the plunger side start to slide over the sliding counterface surface lSlb of the ratchet element side, a succeeding new stop surface 122a of the rack tooth 122 abuts the stop counterface surface lOla of the ratchet element side and allows the setback displacement as shown in FIG. 10. Thus, it becomes possible to release the overload otherwise caused by the excessive projection of the plunger 120 due to the temperature change and others of the engine by returning the plunger 120 by one tooth or several teeth of the rack teeth 122.

(Specific Installation Mode of Ratchet Releasing Mechanism) 100591 Next, a specific installation mode of a ratchet releasing mechanism for releasing the engagement of the ratchet teeth 151 of the ratchet element 150 to the rack teeth 122 of the plunger 120 by a tool pin T, which is the most characteristic part of the ratchet-type tensioner 100 of the present embodiment, will be explained in detail with reference to FIG. 11.

(0060] Firstly, as shown in FIGs. 5 and 11, the ratchet releasing mechanism comprises a tool pin engaging portion 154 provided at the plunger-side frontend area of the ratchet element 150 to abut and engage with a pin edge portion Ti of a tool pin T and a pin inserting hole 1i4 provided in the housing body 110 to insert the tool pin T toward the tool pin engaging portion 154.

(0061] That is, as shown in FIG. 11, the tool pin engaging portion 154 of the ratchet element iso comprises a stepped abutment surface i54a formed between the ratchet teeth 151 arid the ratchet-side convex strip 152 which is a part of the outer circumferential surface of the ratchet element at the plunger-side frontend area of the ratchet element 150 as shown in FIG. 11.

The pin inserting hole 114 of the housing body 110 is provided so as to push back the ratchet element 150 in a direction opposite from the ratchet element biasing direction by prying the stepped abutment surface 154a of the ratchet element 150 by the tool pin P. This arrangement permits a prying force of the tool pin P inserted through the pin inserting hole 114 of the housing body 110 to act on the stepped abutment surface 154a of the ratchet element 150 and to push back the ratchet element 150 in the direction opposite from the ratchet element biasing direction.

(0062] Because the ratchet-type tensioner 100 of the first embodiment of the invention thus obtained has the ratchet releasing mechanism that releases the engagement of the ratchet teeth 151 of the ratchet element 150 to the rack teeth 122 of the plunger 120 and comprises the stepped abutment surface 154a formed in the ratchet element 150 and the pin inserting hole 114 for prying the stepped abutment surface 154a of the ratchet element 150 by the tool pin T, the prying force of the tool pin T inserted through the pin inserting hole 114 of the housing body 110 acts on the stepped abutment surface 154a so as to push back the ratchet element in the direction opposite from the ratchet element biasing direction. Thus, it becomes possible to push and set back the plunger 120 by readily releasing the engagement of the ratchet teeth 151 to the rack teeth 122, so that it is possible to considerably reduce a burden of maintenance works such as positioning and replacement of parts of the ratchet-type tensioner and the timing chain in a condition in which the timing chain is loosened.

(00631 then, because the engagement matching mechanism of the rack teeth 122 and the ratchet teeth 151 is composed of the ratchet teeth 151 provided on the outer circumferential surface of the ratchet element 150 along the sliding direction and the housing-side concave groove 113a provided on the inner circumferential surface of the ratchet-accommodating hole 113 along the sliding direction in the condition of being concavo-convexly engaged and stops the outer circumferential surface of the ratchet element 150 from turning against the inner circumferential surface of the ratchet-accommodating hole 113, it is possible to operate the ratchet mechanism composed of the plunger 120 and the ratchet element 150 securely and stably and to eliminate erroneous operation of the ratchet mechanism by avoiding a twist otherwise caused by erroneous assembly between the rack teeth 122 on the side of the plunger 120 and the ratchet teeth 151 of the ratchet element 150.

(0064) Still more, because the rack teeth 122 of the plunger 120 are formed concavo-convexly respectively by the stop surfaces 122a inclined toward the plunger-advance side and the sliding surfaces 122b inclined toward the plunger-setback side, the ratchet teeth 151 of the ratchet element 150 are formed concavo-convexly respectively by the stop counterface surfaces 151a inclined toward the plunger-advance side and the sliding counterface surfaces iSib inclined toward the plunger-setback side, and the inclination angle 9 of the stop surface 122a is formed to be smaller than the inclination angle a of the sliding surface 122b, it becomes possible to smoothly allow the setback displacement without restricting the move of the plunger 120 in the setback direction while preventing wear and damage such as chipping of the teeth that is prone to occur in the ratchet teeth 151 and the rack teeth 122 when the tension of the chain is excessive after starting the engine and to exhibit excellent durability by avoiding excessive impact on the ratchet biasing spring 160. Thus, the advantageous effects of the first embodiment are remarkable.

(Second Embodiment) [0065] Next, a ratchet-type tensioner of a second embodiment of the invention will be explained with reference to FIGs. 12 through 15.

[0066] Here, FIGs. 12A and 12B are enlarged views of a main part of a ratchet-type tensioner 200 of the second embodiment of the invention, FIG. 13 is a section view taken along a line B-B in FIG. 12B, FIG. 14 is an exploded view of a ratchet element, a ratchet biasing spring and a spring stopping plug and FIGs. iSA and 158 are diagrams explaining a ratchet releasing operation in the second embodiment of the invention.

As compared to the ratchet-type tensioner 100 of the first embodiment described above, the ratchet-type tensioner of the second embodiment of the invention is different in terms of a specific installation mode of the engagement matching mechanism and the ratchet releasing mechanism described above and is not different in terms of the other device configurations, so that the specific installation mode of the engagement matching mechanism and the ratchet releasing mechanism of the second embodiment of the invention will be detailed with reference to FIGs. 12 through 15.

It is noted that the device configurations other than the engagement matching mechanism and the ratchet releasing mechanism of the second embodiment of the invention will be denoted by reading the reference numerals in 100's showing the same or corresponding members in the ratchet-type tensioner 100 of the first embodiment described above while replacing with reference numerals in 200's.

(0067] The engagement matching mechanism described above is constructed by a ratchet element 250 having an oval section as shown in FIG. 13 and a het-accommodating hole 213 formed in a housing body 210 having an oval section (not shown) substantially having the same shape with the ratchet element 250 so as to stop an outer circumferential surface of the ratchet element 250 from turning with respect to an inner circumferential surface of the het-accomrnodating hole 213 provided in a direction orthogonal to the sliding direction of the plunger 220.

This arrangement stops the outer circumferential surface of the ratchet element 250 from turning against the inner circumferential surface of the ratchet-accommodating hole 213 and engages the ratchet teeth 251 of the ratchet element 250 to the rack teeth 222 on the side of the plunger 220 precisely across an entire widthwise range, regardless of the engagement between the rack teeth 222 on the side of the plunger 220 and the ratchet teeth 251 of the ratchet element 250 even when the plunger 220 vibrates during when the engine is driven.

(0068] Then, as shown in FIG. 14, the ratchet element 150 described above has a whole length W which is greater than an outer diameter D thereof. This arrangement suppresses inclination and prevents biased wear of the ratchet element 250, that are otherwise prone to be caused within the ratchet-receiving hole 213 in the sliding direction, even when an overload is applied to the ratchet element 250.

Further, in order to engage with the rack teeth 222 engraved on the side surface of the plunger 220 by homogeneously dispersing the engagement load, the ratchet element 250 of the present embodiment is provided with two ratchet teeth 251 having teeth intervals equal with pitches of the rack teeth 222 and the same tooth height with the rack teeth 222 at the edge area on the plunger side thereof as shown in FIG. 14.

(Specific Installation Mode of Ratchet Releasing Mechanism) [0069] Next, a specific installation mode of a ratchet releasing mechanism for releasing the engagement of the ratchet teeth 251 of the ratchet element 250 to the rack teeth 222 of the plunger 220 by a tool pin T, which is the most characteristic part of the ratchet-type tensioner 200 of the present embodiment, will be explained in detail with reference to FIGs. 14 and 15.

[0070] Firstly, as shown in FIGs. 14 and 15, the ratchet releasing mechanism comprises a tool pin engaging portion 254 provided at the plunger-side frontend area of the ratchet element 250 to abut and engage with a pin edge portion Tl of a tool pin T and a pin inserting hole 214 provided in the housing body 210 to insert the tool pin T toward the tool pin engaging portion 254.

[0071] Than is, as shown in FIG. 14, the tool pin engaging portion 254 of the ratchet element 250 comprises a tapered abutment surface 254a formed by partly cutting away the plunger-side frontend area of the ratchet element 250 toward the rear-end area.

The pin inserting hole 214 of the housing body 210 is provided so as to push back the ratchet element 250 in a direction opposite from the ratchet element biasing direction by pressing the tapered abutment surface 254a of the ratchet element 250 by the tool pin T. This arrangement permits a pressing force of the tool pin T inserted through the pin inserting hole 214 of the housing body 110 to generate a component force that acts on the tapered abutment surface 254a so as to push back the ratchet element 250 in the direction opposite from the ratchet element biasing direction.

[0072] Because the ratchet-type tensioner 200 of the second embodiment of the invention thus obtained has the ratchet releasing mechanism that releases the engagement of the ratchet teeth 251 of the ratchet element 250 to the rack teeth 222 of the plunger 220 and comprises the tapered abutment surface 254a formed by partly cutting away the plunger-side frontend area of the ratchet element 250 toward the rear-endareaandthepin inserting hole 214 forpressing the tapered abutment surface 254a of the ratchet element 250 by the tool pin T, the pressing force of the tool pin T inserted through the pin inserting hole 214 of the housing body 210 generates the component force that acts on the tapered abutment surface 254a so as to push back the ratchet element 250 in the direction opposite from the ratchet element biasing direction.

Thus, it becomes possible to push and set back the plunger 220 by readily releasing the engagement of the ratchet teeth 251 to the rack teeth 222, 50 that it is possible to considerably reduce a burden of maintenance works such as positioning and replacement of parts of the ratchet-type tensioner and the timing chain in a condition in which the timing chain is loosened.

[0073] Then, similarly to the ratchet-type tensioner 100 of the first embodiment described above, the ratchet-type tensioner of the second embodiment can operate the ratchet mechanism composed of the plunger 220 and the ratchet element 250 securely and stably and eliminate erroneous operation of the ratchet mechanismby avoiding a twist otherwise caused by erroneous assembly between the rack teeth 222 on the side of the plunger 220 and the ratchet teeth 251 of the ratchet element 250.

Still more, the ratchet-type tensioner of the second embodiment requires no precise mechanical works for configuring the spline concavo-convex engagement between the ratchet-accommodating hole 113 on the side of the housing body and the outer circumferential surface of the ratchet element 150 as described in the first embodiment and thus permits to considerably reduce the burden of its production.

Thus, the advantageous effects of the ratchet-type tensioner of the second embodiment are remarkable.

[0074] The specific mode of the ratchet-type tensioner of the present invention may take any mode as long as the ratchet-type tensioner comprises the housing body in which theoilpassage fcr supplyingexternalpressureoil is formed, the plunger-accommodating hole formed in the housing body, the plunger slidably projecting out of the plunger-accommodating hole toward the traveling chain, the high-pressure oil chamber formed between the plunger-accommodating hole of the housing body and the hollow portion of the plunger, the plunger biasing spring accommodated in the high-pressure oil chamber to bias the plunger in the plunger projection direction, the ratchet-receiving hole formed within the housing, the columnar ratchet element fittingly inserted into the ratchet-receiving hole and sliding in the direction traverse the advance/setback direction of the plunger, the ratchet teeth provided at the plunger-side front-end area of the ratchet element, the ratchet biasing spring for biasing the ratchet teeth toward rack teeth provided on the side surface of the plunger, the spring stopping plug fitted into the rear-end area of the ratchet-receiving hole to seat the ratchet biasing spring, and the ratchet releasing mechanism for releasing the engagement of the ratchet teeth of the ratchet element to the rack teeth of the plunger, wherein the ratchet releasing mechanism comprises the tool pin engaging portion provided at the plunger-side front-end area of the ratchet element to abut and engage with the pin edge portion of the tool pin and the pin inserting hole provided in the housing body to insert the tool pin toward the tool pin engaging portion.

Then, the ratchet-type tensioner allows the spring stopping washer for seating the ratchet biasing spring to be rigidly and readily assembled to the ratchet-receiving hole without falling out of the ratchet-receiving hole, reduces flapping noise by operating the ratchet mechanism securely and stably in operating an engine and prevents seizure of the plunger.

[00751 For instance, a basic configuration of the housing body in the ratchet-type tensioner of the invention may be any one of what introduces pressure oil supplied from an oil pump to the oil supplying passage formed within the housing body or what is provided with an oil reservoir concavely formed on a back part of the housing bodj to once reserve the pressure oil supplied from the oil pump before introducing the oil supplying passage formed in the housing body.

(0076] In the case of the ratchet-type tensioner of the invention, a check valve unit for blocking a back flow of the pressure oil from the high-pressure oil chamber to the oil supplying passage may be either one which is assembled in a bottom of the plunger-accommodating hole or one which is not assembled in the bottom of the plunger-accommodating hole.

Still more, in the case of the ratchet-type tensioner comprising the check valve unit described above, its concrete unit structure may be any known type as long as it is assembled in the bottom of the plunger-accommodating hole and blocks the pressure oil from flowing back from the high-pressure oil chamber to the oil supplying path.

For instance, the check valve unit may be a type having a ball seat communicating with the oil supplying path for supplying the pressure oil to the high-pressure oil chamber, a check ball seated on a valve seat of the ball seat, a ball biasing spring for pressing and biasing the check ball to the ball seat and a bell-like retainer for restricting a move of the check ball.

[0077] Still more, in the case of the ratchet-type tensioner comprising the check valve unit described above, its concrete unit structure may be any known type as long as it is assembled in the bottom of the plunger-accommodating hole and blocks the pressure oil from flowing back from the high-pressure oil chamber to the oil supplying path.

For instance, the check valve unit may be a type having a ball seat communicating with the oil supplying path for supplying the pressure oil to the high-pressure oil chamber, a check ball seated on a valve seat of the ball seat, a ball biasing spring for pressing and biasing the check ball to the ball seat and a bell-like retainer for restricting a move of the check ball.

[0078] Still more, the engagement matching mechanism of the ratchet tieth of the ratchet element to the rack teeth on the side of the plunger used in the ratchet-type tensioner of the invention may have any configuration as long as it is constructed so as to stop the outer circumferential surface of the ratchet element from turning against the inner circumferential surface of the ratchet-accommodating hole.

For instance, the engagement matching mechanism may be composed of a ratchet-side convex strip formed of a spline such as a rectangular spline and an involute spline provided on the outer circumferential surface of the ratchet element having a circular section along the sliding direction and a housing-side concave groove composed of a spline groove such as a rectangular spline and an involute spline provided on the inner circumferential surface of the ratchet-accommodating hole substantially having the same diameter in the condition of concavo-convexly engaging with the ratchet-side convex strip. The engagement matching mechanism may be also composed of a ratchet-side concave groove formed of a spline groove such as a rectangular spline groove and an involute spline groove provided on the outer circumferential surface of the ratchet element having a circular section along the sliding direction and a housing-side convex strip composed of a spline such as a rectangular spline and an involute spline provided on the inner circumferential surface of the ratchet-accommodating hole substantially having the same diameter in the condition of concavo-convexly engaging with the ratchet-side concave groove. Or, the engagement matching mechanism may be what stops turning by a ratchet element having an oval section and a ratchet-accommodating hole of the housing body substantially having the same oval section with the ratchet element.

[0079] The specific configuration of the ratchet element used in the present embodiment may be what has several ratchet teeth that engage with the rack teeth engraved on the side of the plunger without twisting across the whole tooth width range on the plunger-side front-end area of the ratchet element and has the tool pin engaging portion for abutting and engaging the pin edge portion of the tool pin at the plunger-side front-end area of the ratchet element.

Still more, a specific configuration of the ratchet teeth formed on the ratchet element used in the present embodiment is preferable to be two or more ratchet teeth having teeth distances with equal pitch and equal tooth height because the ratchet teeth can engage with the rack teeth on the side surface of the plunger equally while dispersing a load.

The specific configuration of the tool pin engaging portion provided in the plunger-side front-end area of the ratchet element may be either one of the stepped abutment surface formed between the ratchet teeth and the outer circumferential surface of the ratchet element in the plunger-side front-end area of the ratchet element or the tapered abutment surface formed by cutting away a part of the plunger-side front-end area of the ratchet element toward the rear-end area as long as it permits to release the engagement of the ratchet mechanism composed of the plunger and the ratchet element during its maintenance.

[DESCRIPTION OF REFERENCE NUMERALS]

[0080] 100, 200 ratchet-type tensioner 110, 210 housing body 111, 211 oil supplying passage 112, 212 plunger-accommodating hole 113, 213 ratchet-receiving hole 113a housing-side concave groove 114, 214 pin-inserting hole 120, 220 plunger 121, 221 hollow portion 122, 222 rack teeth 122a stop surface 122b sliding surface 130, 230 plunger biasing spring 140, 240 check valve unit 141, 241 ball seat 141a, 241a oil passage 14th, 241b valve seat 142, 242 check ball 143, 243 ball biasing spring 144, 244 bell-like retainer 150, 250 ratchet element 151, 251 ratchet tooth lSia stop counterface surface iSib slide counterface surface 152 ratchet-side convex strip 153, 253 spring-accommodating hole 154, 254 tool pin engaging portion 154a stepped abutment surface 254a tapered abutment surface 160, 260 ratchet biasing spring 170, 270 spring stopping plug 171, 271 projecting tongue Si driving sprocket 32 driven sprocket C timing chain L movable lever G stationary guide P piston-section high-pressure oil chamber R high-pressure oil chamber D ratchet outer diameter w ratchet whole length Fs biasing force of ratchet biasing spring Ft reaction force setting back plunger on starting engine F2 reaction force setting back plunger when tension of chain is excessive after starting engine component force in sliding direction of ratchet caused by reaction force Fl f2 component force in sliding direction of ratchet caused by reaction force F2 fh component force acting on stop surface of plunger by reaction force F2 0 inclination angle of stop surface formed on plunger a inclination angle of sliding surface formed on plunger T tool pin

500 prior art ratchet-type tensioner

512 housing 514 plunger 516 oil chamber 518 spring 520 oil sub-chamber 524 rod 526 piston 528 air chamber 530 cap 532 air communicating hole 534 second spring 536 engagement teeth 538 rack 544 oil passage 548 oil passage 550 cii reservoir