Hydraulic tensioner

Abstract: A hydraulic tensioner (1) for an engine timing chain includes a housing (2) having a bore (2A). The end portion of a plunger (3) is slidably fitted into the bore (2A). The end of an oil inlet (51) provided in an engine block (5) is fitted with a seal cap (6) having a C-shaped cross section and an outside concavity (61). The hydraulic tensioner (1) utilizes the concavity (61) as an oil reservoir. Oil passages (21,22) are formed in the housing (2) to connect an oil chamber (20) with the concavity (61). The seal cap (6) has an orifice (6A) to connect the oil inlet (51) with the concavity (61). The present invention results in decreased space occupied by and reduced manufacturing cost for a hydraulic tensioner (1) having an oil reservoir (61).

Description: BACKGROUND OF THE INVENTION The present invention relates generally to tensioners used with chain drives in automotive timing and power transmission applications. In particular, the present invention is related to a hydraulic chain tensioner device which has an associated oil reservoir. The oil reservoir is formed between a seal cap located in an engine block or mounting block oil supply passage and the tensioner body. Chain tensioning devices, such as hydraulic tensioners, are used as control devices for power transmission chains as the chain travels between a plurality of sprockets. In an automotive application, the tension of the chain can vary greatly due to the wide variation is the temperature and the linear expansion among the various parts of the engine. Moreover, wear to the chain components during prolonged use can produce a decrease in the tension of the chain. As a result, it is important to impart and maintain a certain degree of tension to the chain to prevent noise, slippage, or unmeshing of the chain with the sprocket teeth. It is especially important in the case of a chain-driven camshaft in an internal combustion engine to prevent the chain from slipping because the camshaft timing can be misaligned by several degrees, possibly rendering the engine inoperative or causing damage. Hydraulic chain tensioners typically have a plunger slidably fitted into the bore of a housing. The space between the hollow plunger and the housing bore forms an oil or fluid chamber. The plunger is biased in a protruding direction outwardly by a spring located in the fluid chamber to provide tension to an associated chain. A lever arm or shoe is often used at the end of the plunger to assist in the tensioning of the chain. A hydraulic tensioner as used with a tensioner arm or shoe is shown in Simpson et al., U.S. Pat. No. 5,967,921. The hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through passages formed in the housing. The plunger is moved outward against the arm and thus, the chain, by the combined efforts of the hydraulic pressure and the spring force. When the plunger tends to move in a reverse direction (inward) away from the chain, typically a check valve is provided to restrict the flow of fluid from the chamber. In such a fashion, the tensioner achieves a so-called no-return function, i.e., movements of the plunger are easy in one direction (outward) but difficult in the reverse direction. In addition, rack and ratchet mechanisms, which are well known in the art are employed to provide a mechanical no-return function. An example of a hydraulic tensioner including the above conventional features and a no-return mechanism is shown in Tada, U.S. Pat. No. 5,860, 881. Typically, oil pressure in the fluid chamber does not rise immediately upon start-up of the engine. This causes an initial insufficient or low oil pressure condition in the oil chamber acting upon the plunger. Poor control of the chain tension and high noise in the chain and associated mechanisms may result during the initial low oil pressure condition. A hydraulic tensioner with an oil reservoir, as disclosed in Japanese Laid Open Patent H6/45141, has been proposed to solve such problems. In such a hydraulic tensioner, a hold for storage of oil, i.e., an oil reservoir, that connects to the oil chamber, is formed in the housing and the oil stored in the oil reservoir is supplied to the fluid chamber in a more timely manner. However, in the conventional hydraulic tensioner with an oil reservoir, due to the need for an oil storage hole in the housing, the housing and overall hydraulic tensioner becomes large compared to the requirement for space saving for the engine. Manufacturing costs are also increased. A hydraulic tensioner has been disclosed by Japanese Laid-Open Utility Model H7/47631, in which the wall of the hydraulic tensioner, for attachment to the engine, is used as a part of the wall of the oil reservoir. A separate concavity for oil storage is formed in the housing. In this example, the manufacturing cost of the unit is high and the overall hydraulic tensioner becomes large. In US-A-3964331 which constitutes the closest prior art and DE-C-4015708 there are disclosed hydraulic tensioners with one way check valves arranged to allow fluid flow into the chamber and prevent fluid flow from the chamber, the valve in each case being formed by a C-shaped member having an orifice and a ball for opening and closing the orifice. In the present invention, a hydraulic tensioner is provided which is less expansive to manufacture and is smaller than conventional hydraulic tensioners while addressing the need for a supplying a ready supply of oil to the tensioner during start-up of the engine. In accordance with the present invention there is provided a reservoir for a hydraulic tensioner for a power transmission chain of an engine system, comprising: a housing having a bore; a plunger slidably received in said bore forming a fluid chamber therebetween;a spring biasing said plunger in a protruding direction from said bore; a first fluid passage extending from a source of oil to said fluid chamber, a seal cap being fitted into said first passage, said seal cap being generally C-shaped in cross section, said C-shape forming an open side and a closed side, said open side being placed facing said chamber, said closed side facing said source of oil and including an orifice, said C-shaped seal cap forming a fluid reservoir to hold fluid for said fluid chamber, characterised in that the orifice is a small orifice arranged to permit reversible passage of fluid through said closed side at a slow rate of flow, and said orifice is sized to retain an amount of fluid on the open side of said C-shaped seal cap when said tensioner is not in operation to pressurise the fluid chamber upon start-up of the engine system. In a preferred embodiment of the invention the seal cap with a C-shaped cross-section having a concavity on its outside surface is mounted at the open end of an oil supply passage provided in the engine block. The concave portion of the seal cap in combination with an outside surface of the tensioner acts as an oil reservoir. An oil passage connects the concavity with an oil chamber formed in the housing. The orifice in the seal cap connects the oil supply passage in the engine block with the concavity formed in the seal cap. The hydraulic tensioner of this invention utilizes the concavity formed in the seal cap, when mounted on the engine block, so that separate formation of an oil storage hold or a concavity in the tensioner housing is unnecessary, thereby reducing manufacturing costs and preventing an increase in the overall size of the housing, thereby saving space. Oil is supplied to the oil reservoir which is the outside concave portion of the seal cap via the orifice formed in the seal cap and the oil supply passage in the engine block. Thus, oil from the oil reservoir is retained in the oil chamber in the tensioner housing after shut down on account of the seal cap and thus oil is available in the fluid chamber, even immediately after re-starting the engine. For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the preferred embodiment of the invention and to the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-section of a hydraulic tensioner of an embodiment of this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to the drawings, FIG. 1 illustrates a preferred embodiment of the present invention. As shown in the cross-section of FIG. 1, hydraulic tensioner 1 comprises a housing 2, in which a bore 2a is opened at one end, a plunger 3, the rear end of which is inserted in bore 2a, and a coil spring 4 applies a force to plunger 3 in the projecting direction. First and second ends of coil spring 4 are press-contacted to the bottom wall of bore 2a and the inner wall of tip 3a of the plunger, respectively. Tip 3a of the plunger is in contact with a tensioner arm (not shown), which is placed on the side of the slack span of the chain (not shown). Oil passages 21 and 22 are formed in housing 2 and oil passage 21 opens to the bottom wall of bore 2a and oil passage 22 opens to the outer wall of housing 2. Main galley or conduit 51, which is an oil supply passage, is formed in engine block 5 and seal cap 6 with a generally C-shaped cross-section is mounted on the open end of this main conduit 51. A concavity 61 is formed by the C-shape of seal cap 6 on the outside of seal cap 6 and orifice 6a is formed at the radial center of seal cap 6. Oil passage 22 is connected to concavity 61. Hydraulic tensioner 1 utilizes concavity 61 as an oil reservoir through the above-mentioned composition. In operation, immediately after engine start-up, a chain is pulled by the drive sprocket and a slight slackening occurs on the side of the slack span of the chain, thereby projecting plunger 3 by the force of coil spring 4. Then, the pressure in oil chamber 20, which is formed by bore 2a and the hollow rear end of the plunger, becomes lower. As a result, the oil stored in concavity 61 flows into oil chamber 20 via oil passages 21, 22. Thereby, the oil pressure caused by oil flowing into oil chamber 20 and the force of coil spring 4 act on plunger 3. When the engine is in operation, the oil in main conduit 51 is led to concavity 61 via orifice 6a and is stored in concavity 61. When the tension of the chain increases during engine operation and a force in the plunger in the direction of retraction acts from the chain onto plunger tip 3a, pressurized oil in oil chamber 20 gradually returns into main conduit 51 from oil passages 21, 22 via orifice 6a of seal cap 6. Thereby, sudden retraction of plunger 3 is prevented. The outside concave space of seal cap 6, which is mounted to the open end of main conduit 51 in engine block 5, is used as an oil reservoir, so that separate formation of an oil storage hold or concave space in housing 2 becomes unnecessary. As a result, the cost of manufacturing such a reservoir is eliminated and the overall size of the housing, is also reduced to save space. Furthermore, an oil reservoir is provided directly to the open end of main conduit 51 without the presence of a by-pass passage, so that the time to supply oil from the main conduit 51 to the oil reservoir can be shortened. As explained above, in the hydraulic tensioner of this invention, the outside concave portion of the seal cap is utilized as an oil reservoir, an oil passage that connects the concavity with the oil chamber is formed in the housing and an orifice that connects the oil supply passage with the concavity is formed in the seal cap, so that separate formation of an oil storage hole or concavity in the housing is unnecessary and reduction of manufacturing costs can be realised, as well as space-saving.

Claims: A reservoir for a hydraulic tensioner for a power transmission chain of an engine system, comprising: a housing (2) having a bore (2a); a plunger (3) slidably received in said bore forming a fluid chamber (20) therebetween; a spring (4) biasing said plunger (3) in a protruding direction from said bore; a first fluid passage (51) extending from a source of oil to said fluid chamber, a seal cap (6) being fitted into said first passage, said seal cap being generally C-shaped in cross section, said C-shape forming an open side and a closed side, said open side being placed facing said chamber, said closed side facing said source of oil and including an orifice (6a), said C-shaped seal cap forming a fluid reservoir (61) to hold fluid for said fluid chamber, characterised in that the orifice is a small orifice (6a) arranged to permit reversible passage of fluid through said closed side at a slow rate of flow, and said orifice is sized to retain an amount of fluid on the open side of said C-shaped seal cap (6) when said tensioner is not in operation to pressurise the fluid chamber upon start-up of the engine system. The reservoir for a hydraulic tensioner for a power transmission chain of claim 1 wherein said orifice (6a) has a diameter substantially smaller than the diameter of said open side of said seal cap (6). The reservoir for a hydraulic tensioner for a power transmission chain of claim 1 or 2 wherein said first fluid passage (51) has a diameter equal to the diameter of said seal cap so that said seal cap is tightly fit in said first passage. The reservoir for a hydraulic tensioner for a power transmission chain of claim 1, 2 or 3 wherein a second passage (22) is formed between said seal cap (6) and said fluid chamber (20) to carry fluid from said source of oil to said chamber, the diameter of said second passage (22) being less than the diameter of the open side of said seal cap. The reservoir for a hydraulic tensioner for a power transmission chain of claim 4 wherein said diameter of said second passage (22) is less than the diameter of said first passage (51). The reservoir for a hydraulic tensioner for a power transmission chain of claim 4 or 5 wherein said second passage (22) is formed in said housing (2) of said tensioner, which can be mounted on the side of an engine block (5). The reservoir for a hydraulic tensioner for a power transmission chain of claim 6,wherein said first passage (51) can be formed in an engine block (5) on the side of which the housing (2) can be mounted.

Inventors: TADA NAOSUMI, TADA, NAOSUMI
Applicants: BORGWARNER MORSE TEC JAPAN KK, BORGWARNER MORSE TEC JAPAN K.K.
Application year: 2000
Main classification: F16H7
IPC codes: F16H7