Spring-loaded, hydraulically damped strut

Abstract

Strut (10) which includes: a first end (12), a second end (14), a cylinder (16) and a piston (18), wherein the piston (18) is mechanically coupled to the first end (12) and the cylinder (16) is mechanically coupled to the second end (14); a fluid chamber (26) formed between the cylinder (16) and the piston (18); a first fluid passage (36) that fluidically couples the fluid chamber (26) and a fluid reservoir (22); a second fluid passage (38) which fluidically couples the fluid chamber (26) and the fluid reservoir (22) via a check valve (40); and wherein the check valve (40) has an open pre-tensioned, movable valve element (42) which is coupled to a balance spring (41); wherein the movable valve element (42) interacts with a valve seat (43) to control fluid flow through the second fluid passage (38); and wherein the movable valve element (42) responds to a pressure from the balance spring (41); characterized in that the first fluid passage (36) includes an annular gap (25) formed between the cylinder (16) and the piston (18).

Description

TECHNICAL AREA

[0001] This disclosure relates to struts, including spring-loaded hydraulically damped struts. BACKGROUND

[0002] A strut is a structural device positioned between two or more elements, providing structural support between them. A strut may incorporate vibration-damping components and thus be capable of providing vibration-damped structural support between two or more elements. Vibration-damping struts can be used in a vehicle system to provide tension in a serpentine drive assembly for an internal combustion engine or as a suspension component.

[0003] Known strut configurations with vibration damping feature a movable piston within a cylinder clamped between a first and a second mounting point to provide a vibration-damped structural support. The piston and cylinder form a fluid chamber that is fluidically connected to a reservoir via a normally closed or pre-tensioned check valve. Normally closed check valves are designed to prevent fluid flow from the pressure chamber into the reservoir, for example, in response to conditions where the first and second mounting points move relative to each other.Normally closed check valves are further designed to allow free flow of fluid from the reservoir into the pressure chamber, for example, in response to conditions where the first and second mounting points move away from each other. Such strut configurations rely on suction to open the check valve and gravity or pressure to close it. Due to the need for suction, some strut movement may, under certain operating conditions, not reduce the chamber pressure sufficiently to open the check valve when a normally closed check valve is used. Furthermore, an undesirable audible noise, e.g.,A rattling sound can be generated when the movement between the first and second attachment points causes the pressure in the fluid chamber to fluctuate and drop to pressure levels low enough to create a suction and open a normally closed check valve, potentially even venting the fluid if the pressures fall below the fluid's saturation pressure.

[0004] A strut with the features according to the preamble of claim 1 is known from US patent 2014 / 0318908A1.

[0005] DE 10 2006 023 315 A1 describes a strut with features according to a similar technology.

[0006] US patent 2009 / 0321203A1 also describes a strut with features based on a similar technology.

[0007] DE 10 2005 048 949 B3 also describes a strut with features according to a similar technology.

[0008] One object of the invention is to create a strut that is intended for vibration damping between two elements and thereby avoids unwanted noise. SUMMARY

[0009] This problem is solved by a strut having the features of claim 1.

[0010] A strut is described, comprising a first end, a second end, a cylinder, and a piston, the piston being mechanically coupled to the first end and the cylinder to the second end. A fluid chamber is formed between the cylinder and the piston. A first fluid passage connects the fluid chamber and a fluid reservoir fluidically, and a second fluid passage connects the fluid chamber and the fluid reservoir fluidically. A check valve has an open, pre-tensioned movable valve element coupled to a balance spring, and the valve element interacts with a valve seat to control fluid flow through the second fluid passage. The valve element responds to pressure from the balance spring. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] One or more embodiments are now described by way of example with reference to the accompanying drawings, of which: Fig. 1 schematically represents a cross-sectional view of a passively activated, spring-loaded and hydraulically damped strut with a novel check valve according to the disclosure, which is a structural element placed between two elements and is capable of providing vibration damping; Fig. 2 according to the disclosure schematically represents a top view of a flow restriction disk associated with the check valve and is a disk-shaped round element with a circular concentric flow passage opening and several concentric, annular and arc-shaped openings; Fig. 3 graphically represents data according to the disclosure which are associated with the fluid pressure in a fluid chamber of an embodiment of a strut; Fig. 4. Graphically represents data according to the disclosure, which are associated with the operation of a known strut which uses a normally closed check valve, and show a single occurrence of a decrease in a fluid chamber pressure and an associated increase in the displacement of a flow control ball of the check valve for the known strut; Fig. 5. Graphically represents data according to the disclosure, which are associated with the operation of a known strut that uses a normally closed check valve, and show the multiple occurrence of a decrease in fluid chamber pressure, which is associated with an increase in the displacement of a flow control ball of the check valve for the known strut and audible noise events; and Fig. 6 graphically represents data according to the disclosure, which are associated with the operation of an embodiment of the strut, which refers to Fig. 1 and Fig. 2 is described and advantageously uses an embodiment of the check valve described herein in a normally open state. DETAILED DESCRIPTION

[0012] With reference to the drawings, in which the depicted items serve only to illustrate certain exemplary embodiments, Fig. Figure 1 schematically shows a cross-sectional view of a passively activated, spring-loaded, and hydraulically damped strut (“strut”) 10, which is a structural element mounted between two elements and capable of providing vibration damping. In one embodiment, the strut 10 can be used as a clamping device coupled to a pulley, which serves as an intermediate gear, for exerting a clamping force on a serpentine drive designed to mechanically transmit torque between a crankshaft of an internal combustion engine and engine ancillary components.

[0013] In one embodiment, the strut 10 has a cylindrically shaped piston 18 inserted into an annular cylinder 16, both of which are arranged within a helical coil spring 20. Alternatively, the piston 18 and the cylinder 16 can have other cross-sectional shapes, e.g., square, rectangular, triangular, or others. The strut 10 has a first eyelet 12 and a second eyelet 14, the first eyelet 12 being attached to an extension element 34 that is attached to the piston 18, and the second eyelet 14 being attached to a base section 51 that is attached to the cylinder 16. The spring 20 forces a separation of the first and second eyelets 12, 14. The first and second eyelets 12, 14 provide mechanical attachment points for two elements to provide vibration damping, the mechanical attachment points being in the form of clevises or other suitable fixings.Thus, the first eyelet 12 can be mechanically coupled to a first of the two elements, and the second eyelet 14 can be mechanically coupled to a second of the two elements to provide structural support and vibration damping between them.

[0014] The piston 18 and the cylinder 16 form a fluid chamber 26 between a second end 27 of the cylinder 16 and a second end 19 of the piston 18. A first end 17 of the piston 18 is mechanically attached to the extension element 34, which is attached at the first attachment point, e.g., at the first eyelet 12. A spring ring 28 is attached to the second end 19 of the piston 18 and causes the movement of the piston 18 in the cylinder 16 to be stopped. The spring ring 28 stops at the maximum expansion point of the piston 18 in the cylinder 16 by engaging with a first inwardly projecting shoulder 15. The spring ring 28 stops at the maximum compression point of the piston 18 in the cylinder 16 by engaging with a second inwardly projecting shoulder 33 near the second end 27 of the cylinder 16.

[0015] A first housing element 30 is a tubular element made of steel or another rigid material, arranged around the piston 18 and the cylinder 16, and lockably coupled to the extension element 34 near the first eyelet 12. A second housing element 24 is a tubular element made of steel or another rigid material, arranged around the piston 18 and the cylinder 16, and lockably coupled to the base section 51 near the second eyelet 14. A tubular elastomer seal 32 is lockably attached at one end to the first housing element 30 and at the other end to the second housing element 24. A closed fluid reservoir 22 is thereby formed and filled with a fluid 23, which is preferably an incompressible fluid.

[0016] The second end 27 of the cylinder 16 is mechanically attached to the base section 51, which is attached to the second eyelet 14. The second end 27 of the cylinder 16 has a transverse bore 48, a longitudinal bore 49 through a first disk 44, and a check valve 40 adjacent to the fluid chamber 26 and fluidically coupled to it when the check valve 40 is in an open state. A valve seat 43 is formed in the first disk 44 at one end of the longitudinal bore 49, which opens into the fluid chamber 26 at the second end 27 of the cylinder 16.

[0017] The check valve 40 has a flow restricting disc 45, a movable valve element 42 and a valve spring 41 and is designed as a normally open valve to allow fluid flow between the fluid chamber 26 and the longitudinal bore 49. Fig. Figure 2 schematically shows a top view of the flow restrictor disc 45, which is a disc-shaped round element having a circular concentric flow passage opening 46 and several concentric, annular, and arc-shaped openings 47. The flow passage opening 46 serves as a first valve seat for the movable valve element 42 when it is in an open position corresponding to the normally open state of the check valve 40. Thus, the check valve 40 is biased in the open state when the movable valve element 42 is in the open position.

[0018] The valve spring 41 is a balance spring, preferably designed as a helical coil spring, which is arranged between the movable valve element 42 and a distal end of the longitudinal bore 49. The valve spring 41 has a spring constant that allows the movable valve element 42 to follow the pressure in the fluid chamber 26. A balance spring is an elastic device made of steel or another suitable elastic material that provides a restoring force proportional to its linear displacement relative to a stagnation point. Known applications of a balance spring include attaching a spring to a balance wheel that oscillates at a resonant frequency as an element of a timekeeping device, e.g., a mechanical watch.The spring constant of the valve spring 41 enables the movable valve element 42 to follow the pressure in the fluid chamber 26 by having a spring constant that is low enough to be overcome by the increasing fluid pressure on the movable valve element 42 in the fluid chamber 26, which is caused by compression of the strut 10, but equally high enough to push the movable valve element 42 into the open position at chamber pressures greater than atmospheric pressure. Therefore, when the strut 10 is subjected to expansion, the valve spring 41 pushes the check valve 40 into the open state; that is, it pushes the movable valve element 42 into the open position in response to a decrease in pressure in the fluid chamber 26, without requiring a vacuum in the fluid chamber 26.Conversely, when the strut 10 is subjected to compression, a certain increase in the fluid pressure overcomes the valve spring 41, and it pushes the check valve 40 into the closed position, i.e., it pushes the movable valve element 42 into the closed position.

[0019] The movable valve element 42 is pre-tensioned in the open position, i.e., it is normally open to allow the fluid 23 to flow through the arc-shaped openings 47 under static pressure and when the pressure between the fluid chamber 26 and the longitudinal bore 49 decreases, for example when a tensile force is applied to the first and second eyelets 12, 14.

[0020] The movable valve element 42 moves in response to this movement into a closed position against the valve seat 43 to interrupt the fluid flow between the fluid chamber 26 and the longitudinal bore 49 when the pressure in the fluid chamber 26 increases above a static pressure. The linear movement of the movable valve element 42 can be on the order of less than 1 mm when moving between the open and closed positions, and in one embodiment it can be as little as 0.1 mm. The arcuate openings 47 are dimensioned with suitable cross-sectional areas and diameters to allow fluid flow under these conditions without interference from pressure changes acting on the movable valve element 42. This includes ensuring that the movable valve element 42 is not prevented from moving against the valve seat 43 in response to pressure changes under these conditions.

[0021] A closed fluid circuit comprises the fluid reservoir 22, a first fluid passage 36, the fluid chamber 26, and a second fluid passage 38, which includes the check valve 40. The first fluid passage 36 is formed as an annular gap 25 between the piston 18 and the cylinder 16. The second fluid passage 38 is formed between the fluid chamber 26 and the fluid reservoir 22 by the check valve 40, which is arranged fluidically parallel to the flow restrictor disc 45. When the check valve 40 is in the open state, it allows fluid flow between the fluid chamber 26 and the fluid reservoir 22 via the second fluid passage 38. When the check valve 40 is in the closed state, it interrupts the fluid flow between the fluid chamber 26 and the fluid reservoir 22 via the second fluid passage 38.Thus, the entire fluid flow between the fluid chamber 26 and the fluid reservoir 22 takes place via the first fluid passage 36.

[0022] When the check valve 40 is normally open and spring-loaded in the open position, it allows flow from the low-pressure fluid reservoir 22 to the fluid chamber 26 during extension of the strut 10. During compression of the strut 10, the fluid pressure in the fluid chamber 26 can generate a force on the movable valve element 42 sufficient to overcome the spring force of the valve spring 41 and thereby push the movable valve element 42 against the valve seat 43 into the closed position.

[0023] The strut 10 described herein advantageously relies on a consistent high pressure associated with compression forces to close the check valve 40, instead of an inconsistent low pressure associated with tensile forces to open the check valve 40. Such a configuration can therefore lead to a reduction in system noise, an improvement in the strut's response time, a reduction in oil venting due to negative pressures, and the possibility of achieving bidirectional damping through the closed fluid circuit when required.

[0024] Fig. Figure 3 graphically represents data associated with the fluid pressure, e.g., the fluid pressure in the fluid chamber 26 of an embodiment of the strut 10. The magnitude of the fluid pressure is shown on the vertical axis, and time is shown on the horizontal axis. The fluid pressure is initially shown as a fluid pressure 312 that is greater than a saturation pressure 310. When the fluid pressure decreases (313) and becomes less than the saturation pressure 310, air dissolved in the fluid materializes in the form of bubbles 314. The presence of air significantly reduces the bulk modulus, or stiffness, of the fluid, since air is compressible. A subsequent increase in the fluid pressure (315) causes the air bubbles to partially or completely dissolve back into the fluid 316.The renewed dissolution of air into the fluid causes a sudden increase in the fluid's stiffness, which can lead to a sudden change in displacement and a corresponding audible knocking in strut 10. A further reduction of the fluid pressure (317) to a pressure 18 lower than a vapor pressure 320 can cause the fluid to change state into a vapor, with associated cavity formation. Vaporization may not occur in one configuration of strut 10 due to the design characteristics of the fluid chamber 26 and other factors.

[0025] Fig. Figure 4 graphically represents data associated with the operation of a known strut that uses a check valve configured in a normally closed state. The upper graph shows a comparison of a strut displacement 420 over an elapsed time 405 of 30 ms and includes measured data representing a longitudinal displacement of the ends of a known strut assembly 422, as well as analyzed data 424 that can be inputted into a system simulator. The lower graph shows the pressure 410 of an incompressible fluid contained in a fluid chamber analogous to the fluid chamber 26 described above, and a corresponding movement of a ball 412, which is associated with the displacement of the ball, disk, or other closing element of the check valve, such displacement resulting in fluid flow through the known check valve in this configuration.A saturation pressure 415 for the fluid is also shown. The results show a single occurrence 418 of a decrease in the chamber pressure 414, which is associated with an increase in the displacement 412, i.e., with an expansion of the ends of the known strut, where the chamber pressure is less than a vacuum of 0.5 bar, which is less than the saturation pressure for the fluid. The associated movement of the ball, i.e., the opening of the known check valve from the normally closed state, is delayed until the forces acting on it are overcome, and occurs after the chamber pressure is less than the saturation pressure for the fluid. The consequence is the occurrence of an audible knocking noise.

[0026] Fig. Figure 5 graphically represents data associated with the operation of a known strut that uses a check valve configured in a normally closed state. The upper graph shows a comparison of a strut displacement 520 over time, shown along the horizontal axis 505, and includes measured data representing the longitudinal displacement of the ends of the known strut assembly 522, as well as analyzed data 524 that can be entered into a system simulator. The lower graph shows the pressure 510 measured in a fluid chamber 514, analogous to the fluid chamber 26 described above, and a corresponding movement of a ball 512, which is associated with the displacement of the ball, disk, or other closing element of the check valve, such displacement resulting in fluid flow through the known check valve in this configuration.A saturation pressure for the fluid 515 is also shown. The results show several events 518, which include a decrease in chamber pressure associated with an increase in displacement, i.e., an expansion of the ends of the known strut, where the chamber pressure is less than a vacuum of 0.5 bar, which is less than the saturation pressure for the fluid. The associated movement of the ball, i.e., the opening of the known check valve from its normally closed state, is delayed until the forces exerted on it are overcome and occurs after the chamber pressure is less than the saturation pressure for the fluid. Each of the indicated events 518 with a decrease in chamber pressure falling below the saturation pressure resulted in an audible knocking sound, which is indicated symbolically.

[0027] Fig. Figure 6 graphically represents data associated with the operation of an embodiment of the strut 10, which refers to Fig. 1 and Fig.2 is described and uses the check valve 40, which is configured in the normally open state. The upper graph shows a comparison of the clamping device strut displacement 620 with respect to the elapsed time 605 and includes measured data 622, which represent the longitudinal displacement of the ends of the strut 10, as well as analyzed data 624, which can be entered into a system simulator. The lower graph shows the pressure 610 in a fluid chamber analogous to the fluid chamber 26 described above, and a corresponding movement 614 of the movable valve element 42, which is associated with a displacement of the movable valve element 42 of the check valve 40, such displacement blocking fluid flow through the check valve 40 in this configuration. A saturation pressure 615 for the fluid is also shown.The results indicate the complete absence of any decrease in chamber pressure associated with an increase in displacement, i.e., in the extension of the ends of the known strut. The corresponding movement of the movable valve element 42, i.e., the closing of the check valve 40 from its normally open state, is also shown. No events accompanied by an audible knocking sound were reported.

[0028] Potential improvements resulting from the implementation of the new passive, spring-loaded, and hydraulically damped strut 10 described herein include a reduction in system noise, an improvement in the strut's response time, and a reduction in oil venting due to negative pressures. Furthermore, it is possible to provide bidirectional damping through the closed fluid circuit.

Claims

[1] Strut (10) which includes: a first end (12), a second end (14), a cylinder (16) and a piston (18), wherein the piston (18) is mechanically coupled to the first end (12) and the cylinder (16) is mechanically coupled to the second end (14); a fluid chamber (26) formed between the cylinder (16) and the piston (18); a first fluid passage (36) that fluidically couples the fluid chamber (26) and a fluid reservoir (22); a second fluid passage (38) which fluidically couples the fluid chamber (26) and the fluid reservoir (22) via a check valve (40); and wherein the check valve (40) has an open pre-tensioned, movable valve element (42) which is coupled to a balance spring (41); wherein the movable valve element (42) interacts with a valve seat (43) to control fluid flow through the second fluid passage (38); and wherein the movable valve element (42) responds to a pressure from the balance spring (41); characterized by , that the first fluid passage (36) includes an annular gap (25) formed between the cylinder (16) and the piston (18). [2] Strut (10) according to claim 1, which further comprises that the check valve (40) is arranged fluidically parallel to a flow restriction disc (45). [3] Strut (10) according to claim 1, wherein the check valve (40) comprises the open pre-tensioned, spring-operated valve element (42): that the check valve (40) is designed to allow flow between the fluid chamber (26) and the fluid reservoir (22) via the second fluid passage (38) when it is in an open state; and that the check valve (40) is designed to interrupt a flow between the fluid chamber (26) and the fluid reservoir (22) via the second fluid passage (38) when it is in a closed state. [4] Strut (10) according to claim 3, wherein the strut (10) is designed to cause a flow between the fluid chamber (26) and the fluid reservoir (22) via the first fluid passage (36) when the check valve (40) is in the closed state. [5] Strut (10) according to claim 1, wherein the balance spring (41) has a spring constant which enables the movable valve element (42) to follow the fluid pressure in the fluid chamber (26). [6] Strut (10) according to claim 5, wherein the balance spring (41) with a spring constant that enables the movable valve element (42) to follow the fluid pressure in the fluid chamber (26) comprises that the movable valve element (42) responds to the pressure of the balance spring (41) of the check valve (40), wherein the pressure of the balance spring (41) of the check valve (40) is overcome by an increase in the fluid pressure at the movable valve element (42) in the fluid chamber (26), which is caused by a compression force exerted on the first and second ends (12, 14) of the strut (10). [7] Strut (10) according to claim 6, wherein the response of the movable valve element (42) to the pressure of the balance spring (41) of the check valve (40) comprises that the balance spring (41) of the check valve (40) has a spring constant which is overcome by an increasing fluid pressure on the movable valve element (42) in the fluid chamber (26) caused by the compression force exerted on the first and second ends (12, 14) of the strut (10). [8] Strut (10) according to claim 5, wherein the balance spring (41) has a spring constant that enables the movable valve element (42) to follow the pressure in the fluid chamber (26), further comprising that the spring constant of the balance spring (41) of the check valve (40) is sufficiently large to push the movable valve element (42) into the open position at chamber pressures greater than atmospheric pressure. [9] Strut (10) according to claim 1, wherein the fluid reservoir (22), the first fluid passage (36), the second fluid passage (38) and the fluid chamber (26) form a closed fluid circuit.

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