Patent Application
20070032322
This invention relates to a hydraulic chain tensioner assembly including a fluid-tight chamber connected to a pressure-controlled supply reservoir.
The chain drive has emerged as the preferred means of operating ancillary components within the modern automotive engine. For example, chain drives have been employed to drive complex valve trains, balance shafts, oil pumps, high pressure fuel injection pumps and water pumps. A dedicated tensioning device has become a virtual necessity to ensure the overall functional performance of a chain drive given the advent of increasing packaging complexity and its influence on chain drive layout and design. Over time, a chain may slacken due to repeated loading and unloading cycles during torque reversal. Hydraulic chain tensioner assemblies must strike a balance in imposing an apply force sufficient to tighten a slack chain to ensure chain functionality, while minimizing chain noise. Noise caused by high apply loads may be referred to as “whine” and “whiz” and is due to abrupt and impulsive engagement and disengagement of the sprocket teeth with successive links of the chain. When tensioner reaction loads are too low, a rattle or clatter noise of the chain impacting against the sprockets and guides occurs.
A hydraulic chain tensioner assembly is provided that achieves low apply loads to minimize whine and whiz noise but is very stiff in reactive loading, which maintains control of the chain while minimizing clatter or rattle type noise.
A hydraulic chain tensioner assembly includes a shoe configured to contact an endless chain. The tensioner body has an opening, which is preferably bored and honed to size, and a plunger is slideably received within the opening. The plunger is connected to the shoe. The plunger and the opening are sized to define a controlled and substantially tight clearance therebetween. The plunger and the opening also at least partially define a substantially fluid-tight chamber. A spring biases the plunger outward from the opening. The tensioner body also has a supply reservoir that is in fluid communication with a fluid source and is also in selective fluid communication with the chamber via a check valve which maintains a fluid column within the chamber. Pressure of fluid in the supply reservoir is substantially independent of the pressure and pressure variations of the fluid source. Notably, an apply force of the shoe upon the chain is a function of stiffness of the spring and not of the pressure of the fluid source. Thus, the hydraulic chain tensioner assembly enables a well-controlled apply force to the chain that is not influenced by pressure variations in the fluid source.
In one aspect of the invention, structure (such as the tensioner body) forms a feed orifice by which fluid communication occurs between the fluid source and the supply reservoir. Other structure, such as a cup plug placed in an opening in the tensioner body above the reservoir, forms a bleed orifice to vent air from the reservoir. The feed and bleed orifices are sized to control pressure of fluid within the supply reservoir.
In another aspect of the invention, the feed orifice is characterized by a first diameter that is larger than a second diameter of the bleed orifice. This enables a substantially constant slight pressurization within the supply reservoir. The feed orifice diameter may also be slightly smaller than the bleed orifice diameter, in which case the reservoir pressure will be the same as that downstream of the bleed orifice (e.g., atmospheric pressure).
In one aspect of the invention, an air vent valve is in communication with the fluid chamber to vent air therefrom, thereby causing the fluid column within the chamber to be substantially air-free and to have a hydraulic stiffness that substantially prevents inward movement of the shoe when under loading by the chain. Preferably, the air vent valve is a piddle valve which enables air, but not the more viscous fluid within the chamber, to vent therefrom.
In one embodiment, a plug is positioned in the opening or bore opposite the shoe. The plug is sized to further define the fluid-tight chamber. The check valve is positioned on the plug. The plug has an integral passage by which the supply reservoir is in fluid communication with the check valve. The plug is press-fit into the opening. The plug may also have an annulus between the integral passage and the supply reservoir.
In yet another embodiment, the plunger defines an internal reservoir between the supply reservoir and the chamber. The plunger may have a fill opening and may at least partially form an annular opening in fluid communication between the supply reservoir and the internal reservoir.
In one aspect of the invention, the check valve permits flow into the fluid chamber when the plunger moves outward, which occurs when force from the spring overcomes force of the chain against the shoe. Additionally, the clearance, check valve and air vent valve permit the fluid-filled chamber to provide a substantially static reaction load when loaded by the chain. This is possible because the clearance between the plunger and the opening is preferably so small that the leak down time of the plunger is extremely long. Thus, the hydraulic chain tensioner assembly supplies a relatively low apply force to take up slack from the chain, the apply force not being influenced by system pressure, and yet provides a very stiff reaction load.
A method of manufacturing a hydraulic tensioner assembly includes providing a tensioner body having a reservoir. The method further includes boring an opening through the tensioner body. Furthermore, the method includes machining a first passage in a plug member. A second passage is then machined to intersect the first passage. A check valve is then seated at the second passage. Finally, the plug member and seated check valve are pressed in one end of the opening. Preferably, the method also includes honing the bored opening and sliding a plunger into an opposing end of the opening to then define a chamber with the opening.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers refer to like components,
Referring to
The plunger 24 has an inner opening 32 which may be bored or otherwise formed therein. The inner opening 32 and the bore 22 in the tensioner body 20 cooperate to define a chamber 34. As will be further described below, the chamber 34 is substantially fluid-tight and, when filled with fluid, is characterized by a hydraulic stiffness that substantially prevents inward movement of the shoe 26 when under loading by the chain 14. The hydraulic stiffness (k) of a fluid or oil column F in the chamber 34 Is define by the following formula:
k=[B *A]/L;
where B=bulk modulus of the fluid or oil, A=plunger cross-section area, and L=effective oil column length (or height). Within the hydraulic chain tensioner assembly 12 of
Oil column stiffness k is highly dependant upon the aeration state of the oil. Even a small amount of air entrained within the oil causes the bulk modulus to significantly decrease. Accordingly, the hydraulic chain tensioner assembly 12 preferably includes an air vent valve 38 which includes a valve member 40 that seats within an opening 42 at the distal end 28 of the plunger 24. Preferably, the air vent valve 38 is a “piddle” or “burp” valve of a small poppet-like configuration that is held against the vent opening 42 by a main spring 46. Other types of valves will accomplish the same goal as a piddle type valve, which is to vent any entrained air within the chamber 34. Entrained air within the chamber 34 will migrate to the high end of the plunger 24. The valve member 40 is free to jiggle, or vibrate, at the opening 42 which allows entrained air to escape, but remains substantially seated to prevent higher viscosity oil from exiting through the opening 42.
Tensioner body 20 is formed with a cavity 48 which may be referred to herein as a supply reservoir. The supply reservoir 48 is preferably cast in the tensioner body 20. An upper opening 50 of the reservoir 48 is capped by a cup plug 52, which creates a leak free closure.
The tensioner body 20 is machined as formed with a feed port 54 which is in fluid communication with a fluid supply passage 56 from the main oil gallery 55 (i.e., a fluid source) of the engine 10. A feed port cup plug 57 seals the feed port 54. The feed port 54 should be located within the upper most region of the reservoir 48 for maximum retained volume for when the engine 10 is shut down and then restarted. Oil flows through the fluid supply passage 56 to the feed port 54. The fluid supply in the fluid supply passage 56 is pressurized by a pump (not shown), as is well understood by those skilled in the art. A feed orifice 58 in the cup plug 57 controls fluid flow into the reservoir 48. A bleed orifice 60 is formed in the plug 52 and is utilized to vent air from the supply reservoir 48. The bleed orifice 60 should also be located at the top of the reservoir 48 to maximize the reservoir volume for optimal venting of entrained air.
The feed orifice 58 and the bleed orifice 60 are sized to create a “feed/bleed” system. The term “feed/bleed” system means a system designed for controlled charging or supply and controlled discharge across a hydraulic element, such as the reservoir 48. The feed orifice 58 essentially controls the net flow into the reservoir 48. The bleed orifice 60 affects the pressure within the reservoir 48. For feed orifice diameter/bleed orifice diameter >1.0, there will be some governed pressure within the reservoir 48 higher than atmospheric (assuming the bleed orifice 60 is vented to atmosphere). For feed orifice diameter/bleed orifice diameter <1.0, the pressure within the reservoir 48 will only attain the pressure downstream of the bleed orifice 60, i.e., with the bleed orifice 60 vented to atmospheric pressure, the reservoir 48 can only attain atmospheric pressure.
Accordingly, in one embodiment, the feed orifice 58 is preferably one to two millimeters (mm) in diameter and the bleed orifice 60 is preferably approximately 2 mm in diameter. Thus, the bleed orifice 60 is at least the same diameter or is a greater diameter as the feed orifice 58. The sizing of the orifices 58, 60 enables a very low reservoir pressure, ideally on the order of 35 kilopascals (kPa) or less (5 pounds per square inch (psi)). Notably, the restriction of the feed orifice 58 creates a pressure drop from the fluid supply passage 56. Alternatively, the ratio of feed orifice diameter/bleed orifice diameter may be slightly greater than 1.0 to affect a very slight pressurization of the reservoir 48 (as described above). (The unseating pressure differential of a check ball valve assembly 70, described below, is designed to coordinate with the chosen ratio of feed orifice diameter/bleed orifice diameter.) A very slight pressure in the reservoir 48 will still yield desired operation. This reservoir pressure is still substantially lower than gallery feed pressure and with less variation. In fact, changes in pressure of the oil supply in the passage 56 are not communicated to the fluid in the supply reservoir 48 due to controlled feeding through the feed orifice 58 and venting of air through the bleed orifice 60 which controls pressure in the reservoir 48.
Within the scope of the invention, alternative reservoir designs may be utilized. For instance, the reservoir may be an “open hopper” design in that the opening 50 at the top of the reservoir 48 may be left open, not closed off by cup plug 52 (i.e., no cup plug 52 is necessary in an “open hopper” design). The opening 50 is positioned upward to catch splashed fluid within the engine 10. (The splashed fluid is delivered from the fluid source and is used for splash cooling of the engine.) No fluid supply passage 56, feed port 54, or feed and bleed orifices 58, 60, respectively, are required. Because the reservoir 48 is open, fluid within the reservoir will be at atmospheric pressure. The opening 50 may also be enlarged to catch fluid over a greater area. A debris screen may be required at the opening 50 to prevent debris from plugging the supply reservoir 48.
First and second fluid passages 62, 64, respectively, are drilled, bored or otherwise created in the tensioner body 20 such that they intersect and the first fluid passage 62 opens to the supply reservoir 48. A seal member 66 seals an end of the first fluid passage 62 opposite the supply reservoir 48. Preferably the first and second fluid passages 62, 64 are located near a bottom portion of the supply reservoir 48 such that gravity feeds fluid from the reservoir 48.
A one way check ball valve assembly 70 is positioned between the fluid-tight chamber 34 and the second fluid passage 64. A check ball 72 is seated on a valve seat 74. The check ball 72 and valve seat 74 are of a “zero leak” design. A check ball spring 76 biases the check ball 72 against the valve seat 74. The check ball spring 76 has a stiffness that allows the check ball 72 to unseat from the valve seat 74 at a very slight pressure differential in the fluid-tight chamber 34. Thus, a slight outward movement of the plunger 24 unseats the check ball 72 and allows fluid to enter the fluid-tight chamber 34 through the first and second fluid passages 62, 64 from the reservoir 48. Thus, whenever slackness develops within the chain 14, the main spring 46 moves the plunger 24 outward; as the plunger 24 extends, the check ball 72 immediately lifts or “unseats” to draw in oil from the supply reservoir 48. The “push” or “apply” force of the plunger 24 and shoe 26 against the chain 14 is dictated principally by the force calibration “i.e. the spring stiffness” of the main spring 46 and is not influenced by engine oil pressure to a large degree (as it is with conventional art). Conversely, when the chain 14 tightens, the reaction force from the plunger 24 and shoe 26 will be dictated by the essentially air-free, fluid-filled column F within the chamber 34. The air-free fluid column F has a hydraulic stiffness k (described above) that substantially prevents inward movement of the shoe 26 and plunger 24 when loaded by the chain 14.
Referring to
Referring to
Referring to
A fluid passage 156 from the main oil gallery is in fluid communication with the supply reservoir 148 through a feed orifice 158 formed in a cup plug 157 positioned at a feed port 154 machined or formed in the tensioner body 120. A bleed orifice 160 is drilled or otherwise formed in the tensioner body 120 at a top portion of the supply reservoir 148. The bleed orifice 160 is preferably at least as large as the feed orifice 158 to maintain a relatively low pressure in the supply reservoir 148, as described with respect to the embodiment of
A one way check ball valve assembly 170 is seated between the fluid-tight chamber 134 and the plunger 124. A check ball 172 is seated against a valve seat 174 by a check ball spring 176. When a main spring 146 biases the plunger 124 outward as slack develops in a chain contacting a shoe 126 at the end of the plunger 124 (chain not shown), the check ball 172 unseats, allowing fluid to flow from the internal reservoir 147 to the fluid-tight chamber 134 at the slightest pressure differential across the check ball valve assembly 170. Fluid from the supply reservoir 148 replenishes the fluid in the internal chamber 147. Because the air vent valve 138 is disposed within the internal reservoir 147 and the supply reservoir 148 fluidly connects with the internal reservoir 147, any entrained air will be vented through the air vent valve 138 and will not reach the fluid-tight chamber 134, thereby maintaining a fluid column F′ therein that maintains stiffness under reaction loading to minimize rattle and clatter of the contacting chain (not shown).
Referring to
Unlike the opening of bore 22 of
A spring 276 with characteristics having an appropriate spring stiffness unseats the check ball 272 from a valve seat 274 when the plunger 224 moves outward during slackening of a chain (not shown) abutting the shoe 226. Thus, fluid from the supply reservoir 248 immediately flows into the chamber 234 to maintain the hydraulic stiffness of the chamber 234.
A method of manufacturing a hydraulic chain tensioner assembly, described with respect to the structure of
The various hydraulic chain tensioner assemblies described above provide an optimal combination of low apply load and stiff reaction loading, enabling a reduction in both chain whine noise and chain rattle and clatter. The very tight plunger to bore clearance of each embodiment affords a very long leak down time of fluid within the fluid-tight chamber. Additionally, variations in fluid supply pressure are divorced from pressure in the supply reservoir through the controlled sizing of the feed orifice and bleed orifice. Thus, apply force of the hydraulic chain tensioner assemblies described above is closely controlled by choosing a main spring with an appropriate stiffness.
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.
