Tensioner equipped with a no-return device and method of disabling anti-rotation device

A hydraulic tensioner is provided with a no-return device and with an anti-rotation device capable of being disabled having a pin, integral with the cylinder of the tensioner, which slides in a first longitudinal slot formed on the outer wall of the piston and a means able to disable the anti-rotation device. The disabling means includes a second slot, at right angles with respect to the first longitudinal slot to which it is connected, situated at the end of the first longitudinal slot nearer to the bottom of the cylinder. The second slot may also be a throat connected to the first longitudinal slot to which it is perpendicular, and which extends for the whole circumference of the piston. The second slot is preferably shaped as a ramp to join the bottom of the first longitudinal slot to the outer surface of the piston.

REFERENCE TO RELATED APPLICATIONS

This application claims priority from European Patent Application No. 04425778.0, filed Oct. 15, 2004, entitled, “HYDRAULIC TENSIONER, EQUIPPED WITH A NO-RETURN DEVICE, COMPRISING ANTI-ROTATION MEANS CAPABLE OF BEING DISABLED AND METHOD OF DISABLING SAID ANTI-ROTATION MEANS” under the benefit of 35 USC § 119 (a)–(d) or § 365(b). The aforementioned application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to the field of tensioners. More particularly, the invention pertains to a tensioner equipped with anti-rotation device capable of being disabled.

2. Description of Related Art

A timing system for an internal combustion engine can be controlled by a chain transmission, in which the chain is wound on two or more sprockets, one of which is a drive sprocket and takes its drive (even indirectly) from the drive shaft to transmit it to one or more driven shafts.

For reasons of adjustment, wear on materials and/or of taking-up of play, it is often necessary to compensate for a certain amount of slack of the chain. It is known to the art to use shoe tensioning devices, in which a shoe is biased with an adjustable force against a branch of the chain.

Various means for biasing the tensioning shoe against the chain are known. The most frequently used means are hydraulic tensioners, where a fixed member (generally a cylinder) is mounted on the engine block and a movable member (generally a piston, mobile inside the cylinder) is slidable with respect to the fixed member and acts against the shoe placed in contact with the chain to tension it. In these tensioning devices, the piston is pushed out of the cylinder towards the shoe disposed against a branch of the chain, by the combined action of a spring and pressurized fluid (generally oil) fed into the cylinder chamber through a check valve. Any slackening of the chain due to the heating, wear, and/or to time is compensated by the piston extending out of the cylinder under the action of the biasing means.

When pressurized fluid to be fed into the cylinder chamber is not available (for example because the engine is stopped or because it has only just been started), the piston is urged by the tension of the chain and can return partially into the cylinder, allowing the chain to slacken. This does not transmit the motion correctly from the drive sprocket to the driven sprockets, compromising the efficiency and the reliability of the timing system and being able to put the engine “out of phase,” an arrangement known to the art, for example from European Patent No. 1,188,955 in the name of the Applicant and herein incorporated by reference. European Patent No. 1,188,955 discloses overcoming the drawback, by coupling the cylinder to a pawl which, interacting with a rack coupled to the piston, prevents the piston from returning into the cylinder when pressurized fluid is not available.

To increase the reliability of a “rack and pawl” no-return device and to prevent the piston from being able to rotate accidentally with respect to the cylinder, thus disengaging the rack from the pawl, anti-rotation means or devices are usually provided such as, for example, a closed longitudinal slot, formed on the outside wall of the piston along a generatrix of the piston. A pin, integral with the cylinder and slidable in the longitudinal slot of the cylinder, engages with closed longitudinal slot.

The anti-rotation means or device further prevents the piston from accidentally slipping out of the cylinder. But, when a tensioner is removed from an engine, the anti-rotation means do not allow, without involving actions which are normally long and expensive, the piston to be returned into the cylinder. For example, facilitating the transport and the storage of the tensioner and/or re-using the tensioner for another engine involves actions which are normally long and expensive.

An object of the present invention is to overcome the above drawbacks by providing a hydraulic tensioner whose piston can be made to return easily into the cylinder by an operator by rotating the piston around its longitudinal axis to disengage the rack from the pawl.

SUMMARY OF THE INVENTION

A hydraulic tensioner is provided with no-return device and an anti-rotation device which may be disabled to disengage the piston of the hydraulic tensioner from the no-return device. A method of disabling the anti-rotation device is also disclosed.

The hydraulic tensioner is provided with a no-return device and with an anti-rotation device or means capable of being disabled. The anti-rotation device includes a pin, integral with the cylinder of the tensioner, which slides in a longitudinal slot formed on the outer wall of the piston and a means able to disable the anti-rotation device. The disabling means or device includes a second slot, at right angles with respect to the first longitudinal slot to which it is connected, situated at the end of the second longitudinal slot nearer to the bottom of the cylinder, or a throat connected to the first longitudinal slot to which it is perpendicular, which extends for the whole circumference of the piston. The second slot is preferably shaped as a ramp to join the bottom of the longitudinal slot to the outer surface of the piston.

DETAILED DESCRIPTION OF THE INVENTION

In the appended figures, corresponding elements are identified by the same reference numerals.

FIG. 1is a perspective view of a first embodiment of a piston3for a hydraulic tensioner, where the slot in which the pin12(FIG. 2) slides is L-shaped and includes a first longitudinal slot6and a second or further slot11(connected to the longitudinal slot6at a right angle, and preferably shaped as a ramp to join the bottom of the longitudinal slot6to the outer surface of the piston3) situated at the end of the longitudinal slot6nearer the bottom of the cylinder2, seeFIG. 2.

FIG. 2is a diagrammatic sectional view of a hydraulic tensioner1(of a type known in the art, for example, from European Patent No. 1,188,955), equipped with a piston3according to the invention.

The hydraulic tensioner1includes a cylinder or a housing2and a piston3housed slidably in a bore of the cylinder, the piston forming a cylindrical chamber4with the cylinder2. The piston3bears the rack5which interacts with the pawl carried by the cylinder2. The pawl5and the rack7form the no return means, allowing movement of the piston in a protruding direction and preventing movement in a retracting direction. The piston3is hollow on the inside and houses a pushing spring8acting between the head end9of the piston3and the bottom of the cylindrical chamber4, which is in communication with a circuit for supplying pressurized fluid, generally oil, through an aperture10and a no-return valve, (not shown, but as known in the prior art).

The combined action of the spring8and the pressurized fluid in the chamber4biases the piston3out of the cylinder2, so that the piston3comes to bear with its head end9against a shoe (omitted in the figure for the sake of simplicity and thus keep the chain taut. Also shown inFIG. 2is a pin12engaged in the longitudinal slot6and the further slot11.

For the sake of simplicity of the graphic representation, in the following figures only the cylinder2, the piston3, the rack5, the longitudinal slot6, the pawl7and the pin12are indicated by reference numerals.

FIG. 3is a diagrammatic sectional view of the hydraulic tensioner1, with the piston3completely extracted from the cylinder2. The condition is easily obtained when the tensioner1is not connected to the engine and the piston3spontaneously protrudes from the cylinder2under the effect, for example, of the spring8(FIG. 2) and/or of its own weight.

InFIG. 3the pawl7is engaged with the final portion of the rack5and the pin12, engaged with one end of the longitudinal slot6, prevents the piston3from slipping out of the cylinder2.

FIG. 4is a diagrammatic sectional view of the hydraulic tensioner1ofFIG. 3, in which the anti-rotation means6,12have been disabled by rotating the piston3around its longitudinal axis to insert the pin12in the further slot11to disengage the rack5from the pawl7. The slot11is preferably shaped as a ramp (FIG. 1).

InFIG. 4the pin12is held in place by a flexible foil13also shown inFIG. 6) applied to the outer surface of the cylinder2. The pin12, having come out of the longitudinal slot6, has moved into contact with the outer surface of the piston3.

FIG. 5is a diagrammatic sectional view of the hydraulic tensioner1with the piston3completely retracted inside the cylinder2and locked therein by rotating the piston3to engage the pawl7with the rack5. The pin12is engaged with the other end of the longitudinal slot6and the further slot11is visible. This configuration is advantageous for the transport and the storage of the hydraulic tensioner1.

FIG. 6shows a side view of the hydraulic tensioner1ofFIG. 5.FIG. 6shows the cylinder2, the piston3completely inserted in the cylinder2and the flexible foil13, which holds the pin12in place.

In a preferred embodiment shown inFIG. 6, the flexible foil13has two opposite flaps15, which are L-shaped and are at least partially overlapping. InFIG. 6, the flaps15are slightly parted and allow the pin12beneath to be seen.

A method for disabling the above mentioned anti-rotation means6,12includes the steps of extracting the piston3from the cylinder2to bring the pin12to one end of the longitudinal slot6level with the further slot11(FIG. 3) and rotating, for example in a clockwise direction, the piston3with respect to the cylinder2to bring the pin12into the further slot11, thus disengaging the pawl7from the rack5(FIG. 4).

At this point the piston3can be made to return inside the cylinder2and fixed there by rotating the piston3in the opposite direction, for example counter-clockwise (FIGS. 5 and 6).

FIG. 7shows a perspective view of a second embodiment of a piston3′ for a hydraulic tensioner made according to the invention, which differs from that illustrated inFIG. 1essentially in that the slot6is not L-shaped but ends in a throat14, perpendicular to the longitudinal slot6, which extends for the entire circumference of the piston3′.

A method for disabling the anti-rotation means6,12does not differ from that described previously with reference toFIGS. 1–4and is shown summarily inFIG. 8, which is a diagrammatical sectional view of the hydraulic tensioner1with the piston3′ completely extracted from the cylinder2, the pin12in the throat14and the rack5engaged with the pawl7and byFIG. 9, which shows diagrammatically, in cross section, the hydraulic tensioner1with the piston3′ completely extracted from the cylinder2, the pin12in the throat14and the piston3′ rotated to disengage the rack5from the pawl7.

FIG. 10shows a side view of the hydraulic tensioner1with the piston3′ completely retracted into the cylinder2. InFIG. 10, the hole16(occupied by the pin12) and the hole17, which shows an area of the longitudinal slot6beneath, are formed in the sleeve of the cylinder2.