VARIABLE FORCE TENSIONER WITH SECONDARY PISTON RATCHET CLIP

Abstract

In order to prevent noise, a ratchet clip and grooves for the ratchet clip to engage are added to the second piston, such that the second piston cannot hit the bottom of the second bore housing. The second piston is prevented from hitting the bottom of the second bore housing by the ratchet clip engaging the ratchet grooves on the outer circumference of the second piston.

Claims

1. A passive tensioner system for tensioning a span of a chain or a belt comprising: a tensioner arm comprising: a body having a first sliding surface in which the chain or belt slides, a second surface opposite the first surface, and a cavity for receiving an external spring; and a tensioner comprising: a housing having a first axially extending bore with a first fluid input and a second axially extending bore with a second fluid input; a first piston slidably received by the first axially extending bore, forming a first pressure chamber in fluid communication with the first fluid input between the first piston and the first axially extending bore, the first piston comprising a body having a first end and a second end; a first piston spring received within the first pressure chamber between the first piston and the first axially extending bore biasing the first piston away from the housing; a second piston slidably received within the second axially extending bore, the second piston comprising a body having: an open end; a closed end; a bottom surface at the open end; a top surface at the closed end; an outer circumference having a series of grooves extending a length along the outer circumference between the open end and the closed end of the body; and a hollow interior having an inner diameter; the second axially extending bore forming a second pressure chamber defined between the inner diameter of the second piston and the second axially extending bore, in fluid communication with the second fluid input through a check valve; a second piston spring in the second pressure chamber, the second piston spring having a first end in contact with the second piston and a second end in contact with a bottom of the second axially extending bore, biasing the second piston away from the housing; an expandable clip engaging the series of grooves on the second piston; wherein when dynamic load from the chain or belt moves the first piston and the second piston inwards and outwards from the housing, fluid from the second fluid input is drawn into the second pressure chamber through the check valve as the second piston is moved outwards from the housing by the second piston spring, and creating a fluid pressure in the second pressure chamber as the second piston moves inward, causing the second piston to exert an outward force on the external spring of the tensioner arm, opposing an inward force of the dynamic load from the tensioner arm; wherein during engine startup and when oil pressure in the second pressure chamber is low, the second piston is prevented from engaging the second axially extending bore by the expandable clip engaging the series of grooves on the second piston.

2. The tensioner system of claim 1, wherein one of the ratchet grooves is a stop groove.

3. The tensioner system of claim 1, further comprising a first check valve in the first fluid input and a second check valve in the second fluid input.

4. The tensioner system of claim 1, wherein the first fluid input is connected to the second fluid input.

5. The tensioner system of claim 1, wherein the first piston spring has a greater stiffness than the second piston spring.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0021] FIG. 1 shows a perspective view of a prior art dual hydraulic tensioner.

[0022] FIG. 2 shows a front view of the prior art dual hydraulic tensioner of FIG. 1.

[0023] FIG. 3 shows a sectional view of the prior art dual hydraulic tensioner of FIG. 2.

[0024] FIG. 4 shows a perspective view of a dual hydraulic tensioner of an embodiment of the present invention.

[0025] FIG. 5 shows an alternate perspective view of the dual hydraulic tensioner of an embodiment of the present invention.

[0026] FIG. 6 shows a close-up of the second piston and the associated ratchet clip of the dual hydraulic tensioner.

[0027] FIG. 7 shows a sectional view of the dual hydraulic tensioner of an embodiment of the present invention with a tensioner arm.

DETAILED DESCRIPTION OF THE INVENTION

[0028] During engine startup or engine failure, there is a lack of inlet oil pressure available to provide to the second high pressure chamber of the second piston and the second piston can bottom out or hit the bottom of the second bore housing in which the second piston is located. The hitting of the second piston on the bottom of the second bore can cause significant noise.

[0029] In an embodiment of the present invention, in order to minimize noise, a ratchet clip and grooves for the ratchet clip to engage are added to the second piston, such that the second piston is prevented from hitting the bottom of the second bore housing by the ratchet clip engaging the ratchet grooves on the outer circumference of the second piston.

[0030] FIGS. 4-7 show tensioners using a passive control system to maintain tension of a chain span or belt. Passive control is defined as a system in which no feedback and a controlled actuator is used to regulate the position of the tensioner pistons.

[0031] The tensioner systems of the present invention include a tensioner (described in further detail below) for a closed loop chain or belt drive system as might be used in an internal combustion engine. It may be utilized on a closed loop power transmission system between a driveshaft and at least one camshaft or on a balance shaft system between the driveshaft and a balance shaft. The tensioner system may also include an oil pump and may also be used with fuel pump drives. Additionally, the tensioner system of the present invention may also be used with belt drives.

[0032] The tensioner tensions the chain or belt (not shown) through a tensioner arm or shoe 402.

[0033] The tensioner includes a housing 502 having a first axially extending bore 502a parallel to a second axially extending bore 502c. While the second bore 502c of the housing 502 is shown as being parallel to the first bore 502a, the second bore 502c may be perpendicular to the first bore 502a or at some other angle relative to the first bore 502a.

[0034] Slidably received within the first axially extending bore 502a is a first piston 503. The first piston 503 has a body with a first end 503a, a second end 503c, and a hollow interior 503b with a closed interior first end 503f. Present within the hollow interior 503b of the first piston 503 is a first piston spring 504. The first piston spring 504 has a first end 504a in contact with the closed first end 503d of the first piston 503 or a volume reducer or vent 505 and a second end 504b in contact with an inlet check valve 508 or bottom 502e of the bore 502a. A first pressure chamber 511 is formed between the first piston 503 and the first axially extending bore 502a. Fluid is supplied to the first pressure chamber 511 through a first supply 506 through an inlet check valve 508. The inlet check valve 508 may be formed of a retainer 552 containing a spring 551 biased cup 553. The first piston 503 is biased outwards from the housing 502 to bias the chain (not shown) through the first end 503a of the first piston, through the tensioner arm by the force of the first piston spring 504 and the pressure of oil in the first pressure chamber 511.

[0035] Alternatively, the first piston 503 could be solid, and in that case the first piston spring 504 would contact a bottom of the solid body of the first piston 503 and the bottom 502b of the first axially extending bore 502a or the inlet check valve 508.

[0036] The second axially extending bore 502c slidably receives a second piston 660. The second piston 660 has a body with a first end 660a, a second end 660c, an outer circumference with a series of ratchet grooves 612, including a stop groove 613, and a hollow interior 660b with a first end 660d. The first end 660d can be closed or can include a vent. The ratchet grooves 612 receive an expandable clip 670 which can ratchet between the grooves 612. When the clip 670 is received within the stop groove 613, the second piston 660 is prevented from extending further out from the housing 502.

[0037] Present within the hollow interior 660b is a second piston spring 666 for biasing the second piston 660 outwards from the housing 502. The second piston spring 666 has a first end 666a in contact with the first end 660d of the interior 660b of the second piston 660 and a second end 666b in contact with the bottom 502d of the second axially extending bore 502c or alternatively a check valve. While not shown, a volume reducer may be present within the interior 660b of the second piston 660.

[0038] A second high pressure chamber 667 is formed by the hollow interior 660b and the second axially extending bore 502c, within which is the second piston spring 666. Fluid is supplied to the second high pressure chamber 667 through an inlet supply 509 and preferably an inlet check valve 507. Alternatively, the inlet check valves 507, 508 may be ball check valves or disk check valves. The inlet supply 509 may or may not be connected to the inlet supply line 506.

[0039] When the tensioner is tensioning a new chain or belt, during operation, fluid is supplied to the first pressure chamber 511 from the first inlet supply 506 and through an inlet check valve 508. This fluid pressure biases the first piston 503 outwards from the housing 502 in addition to the spring force of the first piston spring 504, which applies tension to a span of the closed loop chain or belt through a tensioner arm, such as tensioner arm 402. At the same time, the second piston 660 is also biased outwards from the second axially extending bore 502c by the second piston spring 666 and fluid supplied to the second pressure chamber 667 from the second inlet supply 509 and through inlet check valve 509, which also applies tension to a span of the closed loop chain or belt through the tensioner arm 402 through cap 405 and associated external spring 404.

[0040] When the tensioner is tensioning a worn chain or belt without high load, during operation, fluid is supplied to the first pressure chamber 511 through the first inlet supply 506 and through an inlet check valve 508. This fluid pressure biases the first piston 503 outwards from the housing 502 in addition to the spring force of the first piston spring 504, which applies tension to a span of the closed loop chain or belt through the tensioner arm 402. At the same time, the second piston 660 is also biased outwards further through the second piston spring 666. Tension is also maintained by the external spring 404 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 503 and second piston 660 would need to be extended further outwards from the housing 502 to bias and adequately tension the chain or belt.

[0041] 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 503 and the second piston 660 inwards towards the housing 502 and then outwards from the housing 502. Excessive inward movement of the second piston 660 is resisted by the seating of the ratchet clip 670 in the ratchet grooves 612 on the outer circumference of the second piston 660. Inward movement of the first piston 503 is resisted by fluid pressure in the first pressure chamber 511 created by check valve 508. During the low tension portion of the tension cycle, the first piston 503 moves outward by the force of spring 504. This causes the piston to pump up, drawing fluid through check valve 508 into the first pressure chamber 511 in the first bore 502a. This causes the first end 503a of the first piston 503 to exert an outward force on the tensioner arm 402 in addition to the force exerted by the second piston 660 through the external spring 404, opposing the inward force of the dynamic load.

[0042] When the oil is present, the pump up action of the second piston 660 is similar to the first piston 503. When oil is present, the ratchet clip 670 prevents excessive motion. The ratchet clip 670 prevents inward motion of the second piston 660 when no oil is present. This will limit the motion of the tensioner arm 402 and the first piston 503.

[0043] When the dynamic chain or belt load decreases, fluid within the second pressure chamber 667 leaks to the engine through the second axially extending bore 502c or through a vent. This leakage reduces the mean pressure present within the second pressure chamber 667.

[0044] It should be noted that at all operating conditions, the pressure in the second pressure chamber 667 will pump up to maintain a minimum preload in the external spring 404 on the cap 405. When the force or preload in the external spring 404 gets too low, the second piston 660 moves out from the housing 502, due to the second piston spring 666 and pressure in the second pressure chamber 667 and draws more oil in through the inlet check valve 507.

[0045] Therefore, the first piston 503 in the first axially extending bore 502a provides the dominant damping and hydraulic stiffness and the second piston 660 in the second axially extending bore 502c provides the dominant and automatically adjusting spring force through the external spring 404. 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.

[0046] The tensioner of the present invention decreases noise of the tensioner system caused by the second piston by preventing the second piston from contacting or hitting the bottom of the second bore in the housing by the ratchet clip engaging the grooves on the second piston, preventing the external spring from forcing the second piston further into the housing an amount where the second piston contacts the bottom of the bore of the housing.

[0047] 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.