The present application relates to clutched devices, particularly tensioners, especially for use in vehicles.
Tensioners are used in a variety of applications to apply tension to an endless drive member, such as a belt, that connects a driven rotary member and a drive member. One example of a tensioner in the automobile industry is used to maintain tension in a belt connecting a crankshaft pulley on a vehicle's engine to belt-driven accessories such as an alternator, a water pump, an air conditioning compressor, a power steering pump, and the like. A tensioner is also used to maintain tension in a timing belt that transfers rotary power from the engine's crankshaft to camshafts that control the operation the engine's intake and exhaust valves. Proper operation of the tensioner may increase belt life, the life of the belt-driven accessories in some instances, and can reduce belt-related noises such as belt squeal.
In operation, one or more springs in the tensioner reside in a chamber within the tensioner arm and apply a torque to the tensioner arm in a direction into the belt. Damping elements may be incorporated into the tensioner to assist the tensioner arm in resisting being thrown off the belt during instances when there is a sudden increase in belt tension, as can happen when torsional vibrations are transmitted to the belt through the pulley on the engine crankshaft.
The chamber in the tensioner assembly is typically sealed to the outside environment to prevent ingress of contaminants that would reduce effectiveness and life of the components of the tensioner. However, the action of the torsion spring and damping elements generates heat inside the tensioner, which increases pressure inside the tensioner, which may itself cause damage to some of the components.
Thus, there is a need for a tensioner in which this issue can be at least partially addressed.
There is provided a tensioner, comprising a base that is mountable to an engine block or other structural member, a tensioner arm that is pivotable with respect to the base wherein the base and the tensioner arm together define a cavity, a pulley rotatably mounted to the tensioner arm and configured for engaging an endless drive member, a tensioner spring mounted in the cavity that acts between the base and the tensioner arm to drive the arm in a free arm direction, and a vent structure that opens into the cavity and that permits at least partial equalization of pressure between the cavity and the ambient environment of the tensioner, while inhibiting ingress of contaminants into the cavity.
The vent structure may include a seal with an aperture that opens as a result of a higher pressure in the cavity than exists in the ambient environment and that closes when the pressure in the cavity is substantially the same as the pressure in the ambient environment.
The vent structure may include a membrane that permits the flow-through of gas between the cavity and the ambient environment. The membrane may have one-way permeability to water. The membrane may be arranged to permit water to flow through the membrane out of the cavity. The membrane may inhibit the flow of water through the membrane into the cavity. The membrane may be configured to inhibit water flow into the cavity. The membrane may be configured to inhibit lubricant flow therethrough out of the cavity. The membrane may be configured to inhibit ingress of contaminants into the cavity. The membrane may be configured to have a relatively lower permeability to the passage of oxygen therethrough into the cavity. The membrane may have a relatively higher permeability to the passage of oxygen therethrough out of the cavity.
The vent structure may include an aperture that passes between the cavity and the ambient environment. The aperture may be sized to permit the flow therethrough of gases. The membrane may inhibit the flow therethrough of contaminants when the base is mounted to the engine block. A portion of the aperture may be a groove that extends along an exterior surface of the base and that forms a closed channel when the base is mounted to the engine block. The aperture has an aperture wall that may include an oleophilic coating thereon to inhibit the flow of lubricant through the aperture.
The vent structure may be configured to inhibit the egress of lubricant out of the cavity. The vent structure may be configured to inhibit the ingress of water into the cavity. The vent structure may be configured to facilitate the egress of water out of the cavity.
A detailed description will now be provided by way of example only with reference to the attached drawings, in which:
In this specification and in the claims, the use of the article “a”, “an”, or “the” in reference to an item is not intended to exclude the possibility of including a plurality of the item in some aspects. It will be apparent to one skilled in the art in at least some instances in this specification and the attached claims that it would be possible to include a plurality of the item in at least some aspects.
Reference is made to
A tensioner 24 is provided and is mounted to the engine 10 for engagement with the belt 14 in order to maintain tension in the belt 14. The tensioner 24 is shown in more detail in
The tensioner 24 may include a base 30 that mounts to the engine block shown at 37 or to some other stationary member, a tensioner arm 25 that is pivotally mounted to a spindle 29 that is part of the base 30 for pivotal movement about a tensioner arm axis AA. The tensioner 24 further includes a pivot bushing 27 positioned between the arm 25 and the base 30 (between the arm 25 and the spindle 29 specifically) to facilitate pivoting movement of the tensioner arm 25.
A wheel 16 (which may be, for example, a pulley) is mounted on the tensioner arm 25 for rotation about a wheel axis AW that is spaced from the tensioner arm axis AA. In
A tensioner spring 28 is positioned in a chamber 68 between the tensioner arm 25 and the base 30. The tensioner spring 28 biases the arm 25 in a direction towards the belt 14 so as to engage the wheel 16 with the belt 14 in order to maintain tension in the belt 14. In the embodiment shown the tensioner spring 28 is a torsion spring having a first end 31 that engages a first drive wall (not shown) on the base 30 and a second end 33 that engages a second drive wall (not shown) on the tensioner arm 25. The spring 28 may be axially compressed somewhat in the chamber 68. A thrust washer 32 and a thrust plate 34 are provided to resist axial forced exerted by the spring 28.
A damping structure 23 is provided to dampen movement of the tensioner 24 in particular during sudden increases in belt tension as can occur when torsional vibrations are transmitted into the belt 14 from the engine crankshaft 12.
A dust shield 14 is provided at the bottom of the tensioner 24 to seal against the migration of dust into a central aperture thereof.
The components of the tensioner 10 may be similar to the analogous components of the tensioner 10 shown in PCT publication WO2010037232 and US Patent publication US20090181815, the contents of both of which are incorporated herein by reference.
The belt may be any suitable type of belt, such as, for example, an asynchronous belt such as a single- or poly-V belt, or a synchronous belt that has teeth. While the term ‘belt’ may be used for convenience, it will be noted that any endless drive member may be used.
Some examples of problems that can occur with a tensioner 24 if the cavity 68 becomes overpressurized and/or if certain contaminants are permitted to make their way into the cavity include:
With reference to
The term contaminant is intended to be interpreted broadly, and may include particulate, such as dust and debris, liquids such as liquid water, and gases, such as oxygen in some cases. The vent structure (which may simply be referred to as the ‘vent’) may be provided in several different forms.
In some embodiments, the vent structure 99 includes a seal member with an aperture that is self-closing when the pressure in the cavity 68 and the pressure in the ambient environment outside the tensioner 24 are substantially equal, but that opens to permit the venting of increased pressure that develops in the cavity.
An example of this is shown in
As seen in
The amount of pressure in the chamber 68 that is needed before the seal member 152 lifts away from the surface 151 may be controlled by the properties of the flexible seal member 152 (e.g. durometer and thickness) and the size of the region 153 of the surface 151 that is not adhered to the seal member 152. In other words, selection of the durometer and thickness of the seal member 152 and the size of the region 153 permits adjustment of the pressure required to create the protuberance 157, and therefore adjustment of the desired level of pressure buildup in the chamber 68 before venting occurs.
Another embodiment of a vent structure 99 is shown in
As seen in
As seen in
The amount of pressure in the chamber 68 that is needed before the seal member 152 lifts away from the surface 151 is controlled by properties of the seal member 152, such as durometer and thickness, and the size of the region 163. Tuning the durometer and thickness of the seal member 152 and the size of the region 163 permits adjustment of the pressure required to create the protuberance 167.
With reference to
With reference to
As seen in
In some embodiments, the vent structure 99 includes a membrane, (e.g. a semi-permeable membrane) that permits flow-through of air into and out of the cavity 68 but that prevents the pass-through of contaminants and moisture into the cavity 68.
In embodiments where lubricant exists in the cavity 68, the membrane may be selected to be oleophobic. This may be provided by the membrane itself (i.e. the membrane may have inherent oleophobic properties, optionally by way of an oleophobic substance incorporated within it) and/or it may be provided with an oleophobic coating. An oleophobic membrane will inhibit any lubricant in the cavity from adhering to the membrane thereby reducing the likelihood of any lubricant passing through the membrane to the exterior of the tensioner 24, and also inhibits clogging of the membrane. Other surfaces in the cavity 68 may be coated with an oleophilic coating that promotes the adherence of lubricant thereto, or an oleophobic coating to inhibit the adherence of lubricant thereto, so as to control where lubricant stays and doesn't stay within the cavity 68. Oleophobic membranes are commercially available and may be obtained from Nitto Denko Automotive, Inc., Donaldson Company, Inc., Pan Asian Micro-vent Tech (Changzhou) Co., Ltd. or Able Seal & Design Inc., for example.
U.S. Pat. No. 4,384,725 is hereby incorporated by reference in its entirety. The structure described in that patent includes an oleophobic coating used to assist with preventing the escape of a liquid lubricant from a bearing. Concepts in the '725 patent can be applied to the structure shown in the figures.
Additionally, hydrophobic and/or hydrophilic coatings can be used on the membrane and on other surfaces in the clutched device cavity to control how easily water (both in liquid form and in vapour form) is passed through the membrane. The membrane can be configured to have ‘one-way’ permeability to something such as water, in the sense that it will permit water to pass through the membrane in one direction but not in the other. As a result, any water that migrates into the cavity 68 may be permitted to leave the cavity 68 through the membrane, but water is inhibited from entering the cavity 68 though the membrane. In some embodiments, the membrane may be permeable to water vapour but may be relatively impermeable to liquid water.
Another example is oxygen, whose presence in the cavity 68 can lead to oxidation of the surfaces in the cavity 68. The membrane may be configured to have one-way permeability to oxygen that facilitates the flow of oxygen out of the cavity but that inhibits the flow of oxygen into the cavity 68. Thus, the cavity 68 may have a relatively low concentration of oxygen therein, as compared to the ambient environment.
In an embodiment the vent structure 99 may be as shown in
In another embodiment the vent structure 99 may be as shown in
Vent Provided by passageway
In other embodiments, a passageway that extends from the cavity 68 out to the ambient environment, optionally along a path that is circuitous may be provided. The passageway may be sized to permit gases to flow through it to equalize the pressure between the cavity 68 and the ambient environment, but the circuitous path of the aperture inhibits the entry of contaminants into the cavity 68 therethrough, and also inhibits the flow of water therethrough into the cavity 68. To assist in preventing water to flow into the cavity 68 a hydrophilic coating may be applied to the surfaces of the aperture. Because the coating holds on to water when it is contacted by water, it resists the flow of water therepast. To assist in preventing the flow of lubricant (e.g. oil, grease) out of the cavity 68, the walls of the aperture may be coated with an oleophilic coating, which holds on to oils and the like and thus resists their flow through the aperture, thereby assisting in retaining the lubricant in the cavity 68. The surfaces in the cavity 68 may themselves also be coated to inhibit the oil from reaching the membrane at all. For example, if the lubricant is used between friction surfaces of a damping structure, oleophilic coatings may be used on one or both of those friction surfaces, and an oleophobic coating may be used on other surfaces in the cavity 68 to inhibit oil from remaining on them.
A feature of the path that may be used may be similar to a P-trap in the plumbing industry such that some water would, under gravity, sit in a U-shaped portion of the path and would not progress through the path to the end (i.e. would not drain fully from the path).
In an embodiment, one or more apertures are provided in the bottom of the tensioner (i.e. through the base) at the clamp interface where the tensioner base is bolted to the engine. The holes would intersect with one or more slots molded or machined into the base at the clamp interface between the tensioner base and the engine casting and/or mounting plate.
The orientation and direction of the slots relative to gravity may play a role in the selection of the orientation for the vent slot.
To prevent water or contamination ingress to flow backwards into the tensioner, any such slots would be formed in a labyrinth (also referred to as a tortuous flow path or a circuitous flow path) (e.g. such as a path with many changes in direction or a zig zagged path) in order to mechanically impede the flow or capillary movement action of water back into the tensioner therethrough. This improves the resistance of the tensioner to water that could result from the vehicle negotiating a body of water, or alternatively, as a result of high velocity water impingement resulting from normal road spray and/or vehicle power washing and underbody spray operations.
With reference to
The circuitous path through which air can escape from the cavity 368 is formed by the path between the fastener 351 and the pivot bushing 327 (and/or between the pivot bushing 327 and the wall 371 of the aperture 372, which leads from the chamber 368 to the bottom hollow region 370 of the base 330, a slot 345 that extends from the bottom hollow region 370 to an annular space 374 under a peripheral lip 376 of the cap 335, and finally a slot 355 that extends along a lip 378 of the base 330. Thus, air under pressure in the cavity 368 is able to escape to the ambient environment through the aforementioned path. When pressure in the cavity 310 is equilibrated with the ambient environment, contaminants, including liquid water, have difficulty negotiating the circuitous path to enter the cavity 368.
With reference to
The circuitous path through which air can escape from the cavity 468 includes a cavity aperture 445 in fluid communication with the cavity 468 and a curved groove 411 on an exterior surface at a bottom of the base 330 in fluid communication with an exit aperture 455 to the ambient environment. The curved groove 411 is sealed and forms a closed channel when the bottom of the base 330 is mounted on an engine block 37. Thus, air under pressure in the cavity 468 is able to escape the ambient environment through the exit portion 455. When pressure in the cavity 468 is equilibrated with the ambient environment, contaminants, including water, have difficulty negotiating the circuitous curved groove 411 to enter the cavity 468.
It will be noted that one of more of the vent structures described above may be provided in combination with each other, either in series (whereby one vent structure would connect from the cavity to another vent structure, which would in turn connect to the exterior of the tensioner), or in parallel (whereby each vent structure connects independently between the cavity and the exterior of the tensioner.
While the above description constitutes a plurality of aspects, it will be appreciated that the examples shown and described herein are susceptible to further modification and change without departing from the fair meaning of the accompanying claims.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/705,493 filed Sep. 25, 2012, the contents of which are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/CN2013/083984 | 9/23/2013 | WO | 00 |
Number | Date | Country | |
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61705493 | Sep 2012 | US |