1. Field of the Invention
The invention pertains to the field of tensioners. More particularly, the invention pertains to a tensioner that simultaneously tensions multiple strands of the chain.
2. Description of Related Art
Chain tensioners in engines are used to control the power transmission chains as the chain travels around a plurality of sprockets. The slack of the chain varies as the temperature in an engine increases and as the chain wears. When a chain wears, the chain elongates and the slack in the chain increase. The increase in slack may cause noise, slippage, or tooth jumping between the chain and the sprocket teeth. If the increase of the slack of the chain is not taken up, by a tensioner for example in an engine with a chain driven camshaft, the engine may be damaged because the camshaft timing is misaligned by several degrees due to slippage or tooth jumping.
An example of a tensioner that tensions multiple strands is U.S. Pat. No. 6,322,470. A chain 114 is wrapped around a drive sprocket 110 and a driven sprocket 112 as shown in prior art
a shows the tensioner 210 of U.S. Pat. No. 6,312,351 in the retracted position biasing a blade arm 201.
a shows a tensioner from U.S. Pat. No. 2,210,276. A chain 13 is wrapped around a crankshaft sprocket 12 mounted on the crankshaft 11 and a camshaft sprocket 14 mounted on the camshaft 10. The chain has a drive stretch 15 and a slack stretch 16. A pair of chain followers or shoes 17, 18 with chain engaging surfaces 19, engage the stretches 15, 16. The shoes 17, 18 are pivoted at point 20 to the upper ends of levers 21 which are pivoted at point 22 to the engine block 23. A guide yoke 24 secured to the engine block 23, is arranged at the upper end of levers 21 to retain them in the proper plane of movement. The lower ends of the levers 21 have cammed surfaces 26. The levers 21 may pivot about points 22 such that the shoes 17, 18 are moved toward each other by a fluid motor comprising a piston 27, the upper end which carries a roller 28 that engages the cammed surfaces of the levers 21. The piston fits in a cylinder 29 and is biased outwards by oil from the oil port 31. When oil pressure drops to zero, the oil pressure supporting the piston is withdrawn, and pawls 33 positioned in channeled grooves 38 of the cylinder 29 engage ratchet teeth 32 on the piston 27 as shown in
U.S. Pat. No. 2,129,107 discloses a tensioner for a chain with two arms biasing the chain inwards. Each arm includes a metallic element and a shoe. One end of the arm is pivotally attached to a linkage piece, which is pivotally attached to the engine frame. The opposite end of the arm is biased by a hydraulic shoe positioning member. The two arms are not directly connected to each other.
U.S. Pat. No. 5,702,318 discloses a pair of levers that are interconnected and fixed at one end to the same rotatable base. One of the levers has a convexly curved surface that touches the internal portion of one strand of the chain and is biased by a tensioner. The other lever is also convexly curved and is disposed on the external side of the same strand of the chain. Any force from the tensioner imparted on the first lever also moves the second lever.
US Patent Application Publication No. 2003/0153420 discloses a tensioner with two arms coupled at a first end to a resilient drive and at a second end to a rotatable pulley. The arms are positioned within the pulley to maintain a constant angle between them. The first arm is positioned to form a negative differential angle with respect to the belt and the second arm is positioned to form a positive differential angle with respect to the belt.
A tensioner system imparting tension to a chain comprising a pair of tensioner arms, at least one link piece, and a tensioner. The pair of tensioner arms have a pivoting end for rotation about a fixed pin, a link end, and a shoe with a chain sliding face. At least one link piece has a first end pivotally attached to the link end of each of the tensioner arms. The tensioner has a housing for receiving a piston having an end encompassing a pin that joins the second end of the link pieces together. When the piston of the tensioner is biased outwards from the housing, the end of the piston contacts the pin joining the link pieces of the tensioner arms, moving the tensioner arm toward a chain centerline and tensioning the chain equally on both sides.
A first angle is formed between the link pieces of the tensioner arms when the piston of the tensioner is retracted and a second angle, less than the first angle is formed between the link pieces of the tensioner arms when the piston of the tensioner is biased outwards from the housing.
The tensioner pivots about a shoulder bolt. The piston of the tensioner may be biased outwards from the housing by a spring or a spring plus hydraulic force. The tensioner is located within the strands of the chain between the driven and driving shafts and may be mounted on the chain centerline.
The link pieces are located outside of the strands of the chain and between the driving and driven shafts.
In an alternative embodiment, the tensioner is fixed to the engine block and has a piston with a flat end that contacts the pin joining the links of the opposing tensioner arms.
a shows a prior art tensioner in a retracted position biasing a blade arm 201,
a shows another prior art blade tensioner system.
The tensioner arms have a pivoting end 330a, 330b for rotation about a fixed pin 306a, 306b and a link end 332a, 332b with a pin 314a, 314b for attaching one or two link pieces 318a, 318b that are free to rotate and are located outside the chain strands between the driving and driven sprockets 302, 304.
Inside the chain strands, and preferably on a chain centerline C, is a pivoting tensioner 340 shown in
When the piston 324 is in a retracted position, a first angle is formed between the link pieces 318a, 318b of the opposing tensioner arms 308a, 308b and the tensioner arms 308a, 308b may or may not exert a tensioning force of the chain strands.
When the piston 324 extends outwards from the housing 320, a second angle is formed between the links 318a, 318b of the opposing tensioner arms 308a, 308b, less than the first angle when the piston 324 is in the retracted position, drawing the arms 308a, 308b together towards the chain centerline C, tensioning or squeezing the chain strands between the arms 308a, 308b equally and simultaneously. By linking the arms 308a, 308b together the vibrations of one chain strand is linked to the other chain strand and the vibrations are generally neutralized. By linking the arms 308a, 308b together to a single tensioning force 340, the force is divided equally between both arms 308a, 308b when the strands are equal. Since the arms 308a, 308b are connected, if one strand of the chain tightens, the other strand must slacken. The total tensioning force is applied to resist the tightening strand.
In an alternative embodiment, the pivoting tensioner 340 that pivots about a shoulder bolt 322 would be replaced with a fixed tensioner having a piston with a flat end that contacts the pin that joins the links of the opposing arms, allowing lateral movement of the pin without excessively thrust loading the piston.
The chain tensioner system of the present invention also allows for the additional tensioning necessary to tension a worn, elongated chain 301 as shown in
To tension the elongated, worn chain 301, the piston 324 of the tensioner 340 extends outwards from the housing 320 further, causing the opposing arms 308a, 308b to pull further in towards the chain centerline C and the tensioner 340, squeezing or tensioning the chain's elongated chain strands.
The chain centerline C is defined as a line spaced equidistant between the two strands of the chain.
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.