Hydraulic tensioner

The check valve unit of a hydraulic tensioner comprises a check ball, a ball guide and a disc-shaped retainer. The retainer is fixed to the high pressure oil chamber side of the ball guide by crimping an annular portion of the ball guide over the outer edge of the retainer so that substantially all of an annular circumferential portion of the high pressure chamber side of the retainer is held underneath the crimped portion of the ball guide. The crimped portion of the ball guide forms a recess for receiving and positioning a plunger-biasing spring. A ball seat is similarly secured to the inflow side of the ball guide by crimping.

FIELD OF THE INVENTION

This invention relates to hydraulic tensioners of the type used to apply proper tension to the timing chain or timing belt of an internal combustion engine, and relates more particularly to improvements in the check valve of a hydraulic tensioner.

BACKGROUND OF THE INVENTION

Hydraulic tensioners have been widely used to maintain tension in timing chains and timing belts which transmit rotation from the crankshaft to one or more camshafts of a vehicle engine. By maintaining proper tension, the tensioner prevents vibration of the chain or belt.

A conventional hydraulic tensioner includes a housing having a cylindrical hole, a plunger slidable in the cylindrical hole and protruding from an opening at the end thereof, and a plunger-biasing spring urging the plunger in the protruding direction. The housing and the plunger together form a high pressure oil chamber, and a check valve mechanism, comprising a metal cylinder, is fitted into the cylindrical hole of the housing to permit entry of oil into the high pressure oil chamber, but prevent reverse flow of oil out of the chamber. The check valve mechanism is pre-assembled before being fitted into the cylindrical hole of the housing, and comprises cylindrical element providing an oil passage and having a ball seat formed thereon, a check ball, a coil spring, and a lid. An example of a conventional check valve mechanism is described in Japanese Laid-Open Patent Publication No. 2002-206603 (page 1, FIG. 1).

High machining accuracy is required for production of the conventional check valve mechanism, and assembly of a hydraulic tensioner incorporating the conventional check valve mechanism is difficult.

To address these problems, I have developed the hydraulic tensioner described in my Japanese patent application No. 2003-187277 and depicted inFIGS. 6-7(C)of this application. In this hydraulic tensioner500, the check valve unit540comprises a synthetic resin ball guide542, a ball seat544attached to the ball guide, a check ball541disposed in opposed relationship to the valve seat and guided by the ball guide542, a check ball-biasing spring545, which biases the check ball541toward the valve seat, and a disc-shaped retainer543, which limits the extent to which the check ball541can move away from the ball seat544. As shown inFIGS. 7(A),7(B) and7(C), two protrusions542aare provided on opposite sides of the center of the ball guide542on the high pressure chamber side thereof. An outer circumferential tongue542bis provided on the ball guide for pressing against the wall of the plunger accommodating hole, adjacent the bottom end thereof. Four crimped protrusions542care provided at four locations on the outer circumference of the ball guide at the inlet side thereof. The retainer543is provided with holes543afor receiving the protrusions542a. An oil communication hole543bis provided in the retainer543. A valve seat544ais provided on the ball seat544for abutting engagement with the check ball541, and the ball seat is held in place by the four crimped protrusions542c. The two protrusions542a, which hold the retainer to the ball guide, are inserted into holes543aof the retainer543, and then crimped in order to fix the retainer to the ball guide.

Several problems are encountered in the assembly and use of the check valve structure ofFIGS. 6-7(C). The parts of the protrusions542athat extend through holes543aare liable to become chipped. The width of the crimped portions of the protrusions542ais limited. The end of the plunger-biasing spring530is not fixed relative to the disc-shaped retainer543. Furthermore, it is difficult to position the holes543ain the retainer543so that they receive protrusions542aof the ball guide542. Finally, since the ball seat544is fixed by the four crimped protrusions542cprovided on the outer circumference of the ball guide542, the protrusions542care liable to become chipped. The widths of these protrusions are also limited.

The principal object of this invention is to provide a hydraulic tensioner which can be assembled easily, and in which the check valve unit can be readily assembled and incorporated into the tensioner easily and securely.

SUMMARY OF THE INVENTION

The hydraulic tensioner in accordance with the invention comprises a housing having a plunger-accommodating hole formed therein, and a plunger. The plunger-accommodating hole has an opening at one end thereof and a bottom portion at the opposite end thereof. A plunger is slidable in the plunger-accommodating hole and protrudes through the opening in order to apply tension to a chain, a belt, or a similar traveling, flexible power transmission medium. The plunger and the housing together form a high-pressure oil chamber. The tensioner also includes a plunger-biasing spring, accommodated in the high pressure oil chamber. The spring biases the plunger in a protruding direction. A check valve unit is incorporated into the housing, within the plunger-accommodating hole and adjacent the bottom portion thereof. The check valve unit is arranged to allow flow of oil into the high-pressure oil chamber, and to prevent reverse flow of oil. The check valve unit has an outlet side facing the high pressure oil chamber and an opposite inflow side.

The check valve unit comprises a check ball, a ball seat on which the check ball can be seated to block reverse flow of oil out of the high pressure oil chamber, a ball guide in which the check ball is freely movable toward and away from the ball seat, and a disc-shaped retainer holding the check ball in the ball guide while allowing movement of the check ball within the ball guide toward and away from the ball seat. The disc-shaped retainer has a surface facing the high pressure oil chamber. This surface has an annular peripheral region, and the ball guide has an annular portion on its high pressure oil chamber side. A part of the annular portion surrounds the disc-shaped retainer and a part of the annular portion is crimped over substantially the entirety of the annular peripheral region of the disc-shaped retainer.

In a preferred embodiment, the annular portion of the ball guide forms a recess, and an end portion of the plunger-biasing spring extends into the recess, bears axially against the disc-shaped retainer, and is engaged with the annular portion of the ball guide and held thereby against radial movement.

In the preferred embodiment, the ball seat also has an annular peripheral region and is fixed to the ball guide by an annular crimped portion of he ball guide on the inflow side thereof. This crimped portion is crimped over substantially the entirety of the annular peripheral region of said ball seat.

The hydraulic tensioner of the invention maintains proper tension in a chain, a belt, or other traveling flexible power transmission medium in the same manner as a conventional hydraulic tensioner. However the tensioner exhibits a number of significant advantages over the conventional tensioner.

The disc-shaped retainer is fixed to the ball guide by crimping the ball guide over an annular region that extends substantially entirely around the periphery of the retainer. Accordingly, in contrast with the tensioner shown inFIGS. 6 and 7, in the tensioner according to the invention, the crimped portion of the ball guide provides for a stronger check valve unit, and allows the check valve unit to be assembled without careful positioning of the retainer relative to the ball guide. Furthermore, because the retainer is more securely attached to the ball guide, the check valve unit can be incorporated into the bottom portion of the plunger-accommodating hole without the risk of detachment of the retainer from the ball guide.

An additional advantage afforded by the invention is that the annular portion of the ball guide can form a recess for receiving and reliably positioning an end portion of the plunger-biasing spring, thereby avoiding wear and contact noise which would otherwise result from abnormal contact between the rear end portion of the plunger and the plunger-biasing spring.

A further advantage is afforded where the ball seat is fixed to the ball guide by an annular crimped portion of he ball guide on the inflow side thereof, and the crimped portion is crimped over substantially the entirety of an annular peripheral region of the ball seat. With the ball seat fixed to the ball guide in this manner, the check valve unit can be installed at the bottom portion of the plunger-accommodating hole, without the risk of detachment of the ball seat from the guide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The ball guide of the check valve unit may be composed of a synthetic resin or metal. However, it is preferably composed of synthetic resin so that crimping can be carried out by the application of heat, and assembly of the check valve unit can be carried out quickly and easily.

As shown inFIGS. 1 and 2, a hydraulic tensioner100, in accordance with a first embodiment of the invention, is attached to an engine block adjacent the slack side of a timing chain C, which is in mesh with a drive sprocket S1rotated by a crankshaft of an engine and driven sprockets S2on valve-operating camshafts. A plunger120protrudes through an opening of a cylindrical plunger-accommodating hole111in tensioner housing110, and applies tension to the slack side of the chain C through a pivoted lever L1by pressing against a back surface of the lever at a location remote from the lever's pivot axis. A fixed guide L2guides the travel of the timing chain C on the tension side thereof. Arrows inFIG. 1indicate the directions of rotation of the sprockets and the direction of movement of the chain C.

The exterior of the plunger120is cylindrical, and the plunger fits slidably in the plunger-accommodating hole111. A high pressure oil chamber R is formed by the plunger120and the plunger-accommodating hole111. A coil spring130, serving as a plunger biasing spring, is accommodated within chamber R, and biases the plunger120in the protruding direction.

As shown inFIG. 2, a check valve unit140is incorporated into the tensioner at the bottom of the plunger-accommodating hole111. The check valve unit allows oil, supplied from the engine through a passage (not shown), to flow into the high pressure chamber R, but blocks reverse flow of oil.

The check valve unit140is an assembly comprising a check ball141, a synthetic resin ball guide142, which envelopes the check ball and in which the check ball141is freely movable, a disc-shaped retainer143on the high pressure oil chamber side of the ball guide142for maintaining the check ball141in the ball guide142, and a metal ball seat144, fixed to the ball guide142on the inflow side. The ball is engageable with the seat to block reverse flow of oil out of the high pressure oil chamber R.

The disc-shaped retainer143is fixed to the ball guide142by crimping a portion of the ball guide over the retainer. Crimping a portion of the ball guide over the retainer in this manner provides a stronger assembly than in the case of the hydraulic tensioner500shown inFIGS. 6-7C. When the check valve unit140is incorporated into the plunger-accommodating hole111, there is little risk of detachment of the retainer143from the ball guide. As shown inFIGS. 3 and 4(A), an outer circumferential tongue142bis provided on the ball guide for pressing against the cylindrical side wall of the plunger-accommodating hole111in order to secure the check valve unit in place at the bottom of the plunger-accommodating hole. Oil communication holes143aare bored in the retainer143, as shown inFIGS. 3 and 4(C)

A step-shaped recess143bis formed by the portion of the ball guide that is crimped over the retainer disc. This recess serves as a spring-positioning mounting recess, receiving a rear end of the plunger-biasing spring130. Thus, the spring abuts the retainer143axially, and is reliably held against radial movement by engagement with the annular side wall of the recess143b. By holding the end of the plunger-biasing spring130against radial displacement, the recess prevents wear and contact noise due to abnormal contact between the rear end of the plunger120and the spring.

The ball seat144is also fixed to the inflow side the ball guide142by an annular portion crimped over substantially the entirety of an annular peripheral region of the ball seat. Accordingly, the assembled check valve unit140can be incorporated into the bottom portion of the plunger-accommodating hole111without the risk of detachment of the ball seat144from the ball guide.

Because the ball guide142is used in the high temperature environment of an engine, the ball guide is preferably composed of a polyamide resin such as nylon46, nylon66, glass fiber-reinforced nylon or the like. Crimping is carried out by the application of heat, to soften the resin, and the crimped portions of the ball guide exhibit excellent shape retention.

The retainer143, which maintains the check ball141within the ball guide142and at the same time is in abutting engagement with the rear end of the plunger-biasing spring130, is preferably made of metal.

The check ball141may be composed of metal, ceramic, a synthetic resin, or the like, and has a diameter such that it can moved freely toward and away from the ball seat in the synthetic resin ball guide142, its movement being limited by the ball seat and the retainer, respectively.

In the operation of the tensioner, the high pressure oil chamber R is always filled with oil supplied from the outside through the check valve unit140by an oil pump or the like. When the timing chain C loosens, the plunger120, which is continuously biased in the protruding direction by the plunger-biasing spring130, takes up slack in the chain. As the plunger moves in the protruding direction, the oil chamber R expands, and oil flows into the chamber through the check valve unit140.

When the plunger120is pressed in the retracting direction by an impact force exerted by the timing chain C, the pressure of the oil in chamber R is increased, and the check ball141is pushed against the ball seat144. Consequently, reverse flow of oil from the high pressure oil chamber R through the oil passage144aof the ball seat144is blocked. As a result, the oil pressure in chamber R is further increased, and oil leaks through a slight clearance between the outer circumferential surface of the plunger120and the inner circumferential surface of the plunger-accommodating hole111, and is discharged to the exterior of the tensioner housing110. Consequently, vibration of the plunger120due to the impact force, which acts on the plunger120is quickly damped by flow resistance due to the viscosity of the oil.

As described above, in the hydraulic tensioner100, since the disc-shaped retainer143is fixed to the high pressure oil chamber side of the ball guide142around substantially its entire circumference, the retainer143and the ball guide142can be easily and securely assembled without the need for careful positioning of the retainer143relative to the ball guide142. Furthermore, the retainer and the plunger biasing spring130can be reliably positioned and assembled. Moreover, since the ball seat144is fixed to the inflow side of the ball guide142by crimping about substantially the entire outer circumference of the ball guide142, the check valve unit140can be easily incorporated into the bottom portion of the plunger-accommodating hole111without detachment of the ball seat from the ball guide.

The hydraulic tensioner200, shown inFIG. 5, is also mounted on an engine body in the same manner as tensioner100. Tensioner200is different from tensioner100in that it includes a ratchet mechanism in which retracting movement of the plunger220is blocked by engagement between a rack222formed on the plunger220, and a pawl250pivoted on the tensioner housing210. A ratchet-biasing spring urges the ratchet pawl250toward the rack222. Other features of the tensioner200are the same as those of tensioner100. Therefore, elements of tensioner200that correspond to elements of tensioner100in the series100to144are denoted by corresponding reference numerals in the series200to244.

In the check valve unit240, a disc-shaped retainer243is fixed to a ball guide242by crimping of a portion of the ball guide over substantially the entirety of an annular circumferential area on the high pressure oil chamber side of the retainer. Thus, the check valve unit240is strongly assembled and the length of the crimped region is significantly greater than in the case of the check valve unit in the tensioner ofFIGS. 6-7(C). Detachment of the retainer from the ball guide in the process of installation of the check valve unit in the tensioner housing is reliably prevented.

As in the case of the check valve unit ofFIGS. 2-4(C), a step-shaped recess is formed by the crimped part of the ball guide for receiving and positioning the rear end of the plunger-biasing spring. This spring positioning recess avoids wear and contact noise due to abnormal contact between the rear end of the plunger220and the plunger-biasing spring230.

The ball seat244is fixed to the ball guide on the inflow side by crimping around substantially the entire circumference of the ball seat. Accordingly, the check valve unit240can be reliably incorporated into the bottom portion of the plunger-accommodating hole211, with little risk of detachment of the ball seat244from the ball guide.

The retainer243and the ball guide242can be easily and securely assembled without special efforts to position the retainer243and the ball guide242relative to each other. Moreover, the plunger-biasing spring230is reliably positioned relative to the ball guide during assembly of the tensioner. Furthermore, since the ball seat244is fixed to the ball guide242by crimping around substantially its entire circumference on the inflow side of the ball, the check valve unit240can be easily and securely incorporated into the bottom portion of the plunger-accommodating hole211without detachment of the ball seat from the ball guide.