BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The invention pertains to the field of hydraulic tensioners. More particularly, the invention pertains to a dual hydraulic variable force tensioner with a variable force tensioner arm with a cap disk spring.

DESCRIPTION OF RELATED ART

Dual hydraulic variable force tensioner systems utilize a tensioner arm containing a deep pocket next to a piston pad where a coil spring is retained via an arm button. A secondary piston of the dual hydraulic variable force tensioner contacts the arm cap via a piston and adjusts the spring force when additional mechanical force is required to control the chain drive system via the tensioner arm. The spring rate of the coil spring is significantly higher than the tensioner springs in the dual hydraulic variable force tensioner system to provide increased force with minimal secondary piston extension from the housing of the dual hydraulic variable force tensioner.

SUMMARY OF THE INVENTION

The present inventions places a stack of disk springs between a second piston of a dual hydraulic variable force tensioner system and a hydraulic tensioner arm to allow much higher spring rates if desired. The springs may be stacked in multiple configurations to provide different spring rates. Package space can be reduced depending on the number of springs and orientations of said springs within the tensioner arm.

BRIEF DESCRIPTION OF THE DRAWING Fig. 1 shows a perspective view of dual hydraulic variable force tensioner.

Fig. 2a shows a cut through of a dual hydraulic variable force tensioner with a tensioner arm. Fig. 2b shows a closeup of the cut through of the dual hydraulic variable force tensioner with a tensioner arm of Figure 2a.

Fig. 3 shows a cut through of the tensioner arm.

Fig. 4 shows a closeup along line 4-4 of Figure 3 of the tensioner arm with a Belleville spring set with a spring rate of 400 N/mm.

Fig. 5 shows a tensioner arm with a Belleville spring set with a spring rate of 150 N/mm. Fig. 6 shows a tensioner arm with a Belleville spring set with a spring rate of 100 N/mm. Fig. 7a shows a cut through of a Belleville spring in a first orientation.

Fig. 7b shows a cut through of a Belleville spring in a second orientation.

Fig. 7c shows a top view of a Belleville spring.

DETAILED DESCRIPTION OF THE INVENTION

Figures l-2b show a dual hydraulic variable force tensioner. The tensioner 100 tensions the chain or belt (not shown) through a tensioner arm or shoe 402. The tensioner arm 402 has a first sliding surface 402b in contact with the chain or belt and a second surface 402a opposite the first sliding surface 402b. Along the second surface 402b is a cavity 402c for receiving a spring 404 and a cap 405. The tensioner arm may additionally have an internal flange 407 within the cavity which passes through the spring 404 and centers the spring 404 within the cavity 402c. A first end 404a of the spring 404 is received by the closed end of the cavity in the tensioner arm 402 and the second end 404b of the spring 404 is received by a first surface 405a of the cap 405. The cap 405 is aligned with the first end l60a of the second piston 160 of the dual hydraulic variable force tensioner 100. A second surface 405b, opposite the first surface 405a contacts the second piston 160. Movement of the second piston 160 away from the housing 102 moves the cap 405, compressing the spring 404 and thus moving the tensioner arm 402 towards the chain or belt. While the cap 405 is shown as being U-shaped, any shape may be used that can capture a spring and contact an end of a piston. The tensioner 100 includes a housing 102 having a first axially extending bore l02a parallel to a second axially extending bore l02c. Slidably received within the first axially extending bore l02a is a first piston 103. The first piston 103 has a body with a first end l03a, a second end l03c, an outer circumference l03d and a hollow interior l03b with a closed interior first end 103T The outer circumference l03d has a series of ratchet grooves 112 along the length of the body, with a stop groove 113 near the second end l03c being a larger than the ratchet grooves 112 and capturing a ratchet clip 170. The ratchet clip 170 is an expandable clip that ratchets or expands and contracts in and out of the ratchet grooves 112 as the first piston 103 moves away from the housing 102. The ratchet clip 170 prevents the first piston 103 from moving towards the housing 102 when the tensioner arm or shoe 402 pushes on the first piston 103.

Present within the hollow interior l03b of the first piston 103 is a first piston spring 104. The first piston spring 104 has a first end l04a in contact with the closed interior first end l03f of the first piston 103 or a volume reducer and a second end l04b in contact with a bottom l02b of the first axially extending bore l02a of the housing 102. A first pressure chamber 111 is formed between the first piston 103 and the first axially extending bore l02a. Fluid is supplied to the first pressure chamber through a first supply 106 through an inlet check valve 108. The first piston 103 is biased outwards from the housing 102 to bias the chain through the first end l03a of the first piston, through the tensioner arm 402 by the force of the first piston spring 104 and the pressure of oil in the first pressure chamber 111.

The second axially extending bore l02c slidably receives a second piston 160. The second piston 160 has a body with a first end l60a, a second end l60c, and a hollow interior l60b with a closed first end l60d.

Present within the hollow interior l60b is a second piston spring 166 for biasing the second piston 160 outwards from the housing 102. The second piston spring 166 has a first end l66a in contact with the closed first end l60d of the interior l60b of the second piston 160 and a second end l66b in contact with the bottom l02d of the second axially extending bore l02c. It should be noted that the second piston 160 may have an outer circumference with grooves and receive a ratchet clip and the first piston would have a smooth outer circumference.

A second high pressure chamber 167 is formed by the hollow interior l60b and the second axially extending bore l02c, within which is the second piston spring 166. Fluid is supplied to the second high pressure chamber 167 through an inlet supply 109 and preferably a check valve 107.

When the tensioner is tensioning a new chain or belt, during operation, fluid is supplied to the first pressure chamber 111 from the first inlet supply 106 and through an inlet check valve 108 and biases the first piston 103 outwards from the housing 102 in addition to the spring force of the first piston spring 104, as well as move the ratchet clip 170 within the ratchet grooves 112, biasing a span of the closed loop chain or belt through a tensioner arm 402. At the same time, the second piston 160 is also biased outwards from the second axially extending bore l02c by the second piston spring 166 and fluid supplied to the second pressure chamber 167 from the second inlet supply 109 and through inlet check valve 107 to bias a span of the closed loop chain or belt through the tensioner arm 402 via compression of the spring 404 through the cap 405 within the cavity 402c of the tensioner arm 402 through external spring 404. The inlet check valves 107, 108 may be formed of a retainer 302 containing a spring 304 biased cup 303.

When the tensioner is tensioning a worn chain or belt without high load, during operation, fluid is supplied to the first pressure chamber 111 through the first inlet supply 106 and through an inlet check valve 108 and biases the first piston 103 outwards from the housing 102 in addition to the spring force of the first piston spring 104, biasing a span of the closed loop chain or belt through the tensioner arm 402. At the same time, the second piston 260 is also biased outwards further through the second piston spring 266. Tension is also maintained by the spring biased cap 405 on the tensioner arm 402. As the chain or belt wears further, additional slack is present in the chain or belt span and the first piston 103 and second piston 160 would need to be extended further outwards from the housing 102 to bias and adequately tension the chain or belt. When the tensioner is tensioning a chain or belt during high dynamic chain load, the high cyclic dynamic load force from the chain or belt alternately pushes the first piston 103 and the second piston 160 inwards towards the housing 102 and then outwards from the housing 102. Inward movement of the second piston 160 is resisted by fluid pressure in the second pressure chamber 167 created by check valve 107, and the second piston 160 moves outward by the force of spring 266. This causes the piston 160 to“pump up”, drawing fluid through check valve 107 into the second pressure chamber 167 in the second bore l02c. This causes the first end l60a of the second piston 160 to exert an outward force on the tensioner arm 402 through the spring biased cap, opposing the inward force of the dynamic load.

When the dynamic chain or belt load decreases, fluid within the second pressure chamber 167 leaks to the engine through the second axially extending bore l02c or through a vent. This leakage reduces the mean pressure present within the second pressure chamber 167.

It should be noted that at all operating conditions, the pressure in the second pressure chamber 267 will pump up to maintain a minimum preload in the spring biased cap. When the force or preload in the spring 404 gets too low, the second piston 160 moves out from the housing 102, due to the second piston spring 166 and pressure in the second pressure chamber 167 and draws more oil in through the inlet check valve 107.

Therefore, the first piston 103 in the first axially extending bore l02a provides the dominant damping of the chain span or belt and the second piston 160 in the second axially extending bore l02c provides the dominant and automatically adjusting spring force through the external spring 161. The tensioner of the present invention automatically adjusts the mean tension force to keep the chain or belt tension as low as possible without sacrificing chain or belt control, significantly improving drive efficiency at new chain or belt conditions and conditions with dynamic loads.

During engine startup or engine failure pressure is not present in the second high pressure chamber 167 and the second piston 160 bottoms out or the second end l60c hits the bottom of the bore l02d and causes significant noise. Figure 4 shows a close-up of one arrangement of a spring 404 received between the cavity of the tensioner arm 402 and the cap 405. The spring 404 preferably surrounds an integral flange 407 of the tensioner arm 402. The spring 404 is preferably a plurality of Belleville spring or coned disc spring which may be grouped into sets. The Belleville spring is essentially shaped like a washer which is frusto-conical in shape and is a conical shell which can be loaded along its axis either statically or dynamically. The Belleville spring preferably has a center opening 506 and an outer circumference with an edge 505 as shown in Figure 7c.

Multiple Belleville washers are preferably stacked to modify the spring constant (or spring rate) or the amount of deflection. Stacking individual springs or sets of springs in the same direction will add the spring constant in parallel (same orientation one on top of the other), creating a stiffer joint (with the same deflection). Stacking individual springs or sets of springs in an alternating direction (different orientation) is the same as adding common springs in series, resulting in a lower spring constant and greater deflection. Mixing and matching directions allow a specific spring constant and deflection capacity to be designed.

In Figure 4, a tensioner arm with a spring rate of 400 N/mm biasing the cap 405 is shown. As shown, four sets of Belleville spring sets or cone shaped disk springs with each set 510, 511, 512, 513 comprising two springs are stacked in an alternating fashion (first orientation, second orientation, first orientation, second orientation, etc...), with a first Belleville spring set 510 comprising two springs 504a, 504b, being stacked in a first orientation, a second Belleville spring set 511 comprising two springs 504c, 504d stacked in a second orientation, opposite the first orientation, a third Belleville spring set 512 comprising two springs 504e, 504f stacked in a first orientate on and a fourth Belleville spring set 513 comprising two springs 504g, 504h stacked in the second orientation. The sets of springs 510, 512 of the first orientation are oriented such that an edge 505 of the outer circumference of the springs extends below the center hole 506 of the spring relative to a central axis C as shown in Figure 7a. The set of springs 511, 513 of the second orientation are oriented such that an edge 505 of the outer circumference of the springs extends above the center opening 506 of the spring relative to the central axis C as shown in Figure 7b. Therefore, as shown in Figure 4, the area 507 surrounding the center openings 506 of the first set of Belleville springs 510 (first orientation) contacts the area 507

surrounding the center opening 506 of the second set of Belleville springs 511 (second orientation). The edges 505 of the outer circumference of the third set of Belleville springs 512 contacts the edges 505 of the outer circumference of the second set of Belleville springs 511 and the area 507 surrounding the center opening 506 of the third set of Belleville springs 512 contacts the area 507 surrounding the center opening 506 of the fourth set of Belleville springs 513. In this embodiment, the first set of Belleville springs 510 is adjacent the cap 405 and the fourth set of Belleville springs 513 is adjacent the body of the tensioner arm 402.

Fig. 5 shows a tensioner arm 402 with a spring rate of 150 N/mm biasing the cap 405. In this arrangement, three sets of Belleville or cone shaped disk springs with each set 515, 516, 517 comprising two springs which within the set are stacked in an alternating fashion (first orientation, second orientation, first orientation, second orientation, etc...). The first Belleville spring set 515 comprising two springs 520a, 520b, being stacked in a first orientation and a second orientation within the set, a second Belleville spring set 516 comprising two springs 520c, 520d being stacked in a first orientation and a second orientation within the set, a third Belleville spring set 517 comprising two springs 520e, 520f being stacked in a first orientation and a second orientation within the set. In this embodiment, six individual springs are stacked in alternating orientations between the cap 405 and the body of the tensioner arm 402 within the bore 402c. As described above, in the first orientation, the spring is oriented such that an edge 505 of the outer circumference of the springs extends below the center hole 506 of the spring relative to a central axis C as shown in Figure 7a and in the second orientation, the spring is oriented such that an edge 505 of the outer circumference of the springs extends above the center opening 506 of the spring relative to the central axis C as shown in Figure 7b.

Fig. 6 shows a tensioner arm with a spring rate of 100 N/mm. In this arrangement, , four sets of Belleville or cone shaped disk springs with each set 515, 516, 517, 518 comprising two springs which within the set are stacked in an alternating fashion (first orientation, second orientation, first orientation, second orientation, etc...). The first Belleville spring set 515 comprising two springs 520a, 520b, being stacked in a first orientation and a second orientation within the set, a second Belleville spring set 516 comprising two springs 520c, 520d being stacked in a first orientation and a second orientation within the set, a third spring set 517 comprising two springs 520e, 520f being stacked in a first orientation and a second orientation within the set, and a fourth Belleville spring set 518 comprising two springs 520g, 520h being stacked in a first orientation and a second orientation within the set. . In this embodiment, eight individual springs are stacked in alternating orientations between the cap 405 and the body of the tensioner arm 402 within the bore 402c. As described above, in the first orientation, the spring is oriented such that an edge 505 of the outer circumference of the springs extends below the center hole 506 of the spring relative to a central axis C as shown in Figure 7a and in the second orientation, the spring is oriented such that an edge 505 of the outer circumference of the springs extends above the center opening 506 of the spring relative to the central axis C as shown in Figure 7b.

Since the stiffness of the arm spring affects the dynamic load sharing between the primary and secondary pistons, the spring could additionally be adjusted to optimize damping from the primary piston.

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.