SHOCK ABSORBERS

Description

[0001] The invention relates to a shock absorber, in particular for wheeled vehicles, according to the preamble of claim 1.

[0002] Shock absorbers are used, for example, in the chassis of wheeled vehicles in conjunction with a suspension system to dampen vibrations of the sprung mass and thus allow them to decay quickly. A more accurate term would be "vibration damper," since it is not the shock itself, but rather its effect that is influenced. Shock absorbers are not designed to absorb shocks transmitted to the vehicle from uneven road surfaces; that task falls to the suspension. Shock absorbers are responsible for damping vibrations of the vehicle body onto the suspension as well as vibrations of the wheels onto the tire suspension. Furthermore, shock absorbers are used in a wide variety of applications, such as for vibration damping of machines or machine parts, and also, for example, in furniture manufacturing to dampen flap movements.

[0003] In vehicles, the primary function of a spring within the suspension system is to counteract the mass of the vehicle body and the rider. Two-wheeled vehicles typically use coil springs. The spring force of a coil spring generally exhibits a linear relationship to the compressed travel. At the beginning of a load, it is at rest and supports the weight of the vehicle and rider. A low spring constant (spring rate) ensures a comfortable ride. The spring force increases during the suspension travel. However, a low and comfortable spring constant also allows for rapid and easy bottoming out. Conversely, a high spring constant reduces bottoming out but reduces ride comfort. Light to moderate impacts from uneven road surfaces are absorbed less effectively by a higher spring constant and are transmitted through the vehicle to the rider.The negative suspension travel (rebound damping) results from the weight of the rider and vehicle. Further compression (compression damping) occurs due to the effects of road surface irregularities. The rider's weight can be adjusted by changing the preload of the coil spring.

[0004] By designing a shock absorber in both the rebound and compression directions, driving dynamics and thus ride comfort can be influenced. During the rebound stage of a shock absorber, the vehicle's suspension is damped during the relaxation phase of an oscillation. During the compression stage, the compression velocity is damped.

[0005] Shock absorbers in vehicles are typically hydraulic telescopic shock absorbers. These operate on the principle that the resistance to the flow of the displaced oil depends on the flow velocity. Within the shock absorber, hydraulic oil is forced through narrow bores and valve systems via a piston. The damping force, which counteracts the damper velocity, increases progressively with increasing compression or rebound speed of the piston.

[0006] A disadvantage of the previously known hydraulic shock absorbers (which, as explained above, are actually vibration dampers) is that, in a spring-damper arrangement, their vibration damping impairs the shock-absorbing effect of the spring in its freely oscillating central section. This impairment depends on the piston speed.

[0007] To address this problem, DE 20 2023 102 485 U1 presents a shock absorber in which the shock-absorbing effect of an arranged suspension in its freely oscillating central region is avoided. For this purpose, a piston rod is arranged in a cylinder, passing through it and equipped with two spaced-apart pistons. Axial bores are provided in these pistons, radially spaced around the circumference of the piston rod. A sealing disc for closing the axial bores of the respective piston is axially movably mounted on the piston rod on the outer surface of each piston. The inner wall of the cylinder has, at least in certain areas, a diameter that changes continuously in the axial direction, thereby creating displacement-dependent damping that minimizes vibration damping in the freely oscillating central region of the suspension.This shock absorber has proven itself in practice and enables, for the first time, path-dependent damping with a largely undamped zero position.

[0008] However, when using such a shock absorber, it has been shown that changes in damping behavior can occur under high loads. Further designs of vibration dampers are described in EP 3 458 739 B1 and US 5,376,135.

[0009] The invention aims to remedy this problem. The invention is based on the objective of providing a shock absorber of the aforementioned type which exhibits substantially consistent damping behavior even under high loads. According to the invention, this objective is achieved by a shock absorber with the features of the characterizing part of claim 1.

[0010] Surprisingly, it was found that a high load causes an increase in the fluid temperature inside the cylinder. Due to the incompressibility of the fluid, in this case a hydraulic oil, this results in a pressure increase within the cylinder, which is the cause of the change in damping behavior. The presence of at least one pressure equalization element in the cylinder, which has a pressure-dependent variable volume and is in contact with the fluid, counteracts this pressure increase within the cylinder in the event of a temperature increase in the fluid, particularly a hydraulic oil. When the pressure increases, the pressure equalization element is compressed, releasing additional volume within the cylinder and thus equalizing the pressure. In this way, the pressure equalization element maintains a constant pressure within the cylinder.

[0011] At least one pressure equalization element is made of elastomeric foam, sponge rubber, or cellular rubber. These materials have cavities that are compressed when external pressure is applied, thereby reducing the volume of the pressure equalization element.

[0012] In one embodiment of the invention, a pressure equalization element is arranged between the two pistons, at least partially surrounding the piston rod. This provides an alternative or additional pressure equalization volume.

[0013] In a further embodiment of the invention, at least two radially projecting support elements, spaced apart from each other, are provided between the pistons, and at least one pressure equalization element is held between them. The support elements hold the pressure equalization element in position, allowing the hydraulic fluid to flow freely during operation.

[0014] The inner cylinder wall is formed by the inner surface of at least one damper sleeve inserted into the cylinder, the outer diameter of which is smaller than the inner diameter of the cylinder. At least one pressure equalization element is arranged in the gap formed between the cylinder and the at least one damper sleeve, and the gap can be supplied with fluid via at least one through-hole. This provides a pressure equalization volume along the cylinder wall as the fluid pressure increases. The pressure equalization element is compressed by hydraulic fluid flowing in through the through-hole at an overpressure, thereby compensating for the overpressure.

[0015] In one embodiment of the invention, the cylinder is closed at one end, with the piston rod protruding from the other end. A piston guide is arranged between the two pistons, the guide having at least one pressure equalization opening. This allows for a damper design that reduces installation space. The piston guide ensures linear guidance of the double piston and the piston rod. Simultaneously, pressure equalization between the two pistons can occur through the at least one pressure equalization opening.

[0016] In a further embodiment of the invention, at least one damper sleeve forming the inner wall of the cylinder is arranged on each side of the piston guide. A gap is formed through this sleeve, in which a pressure equalization element is arranged. This provides a pressure-dependent variable volume for pressure equalization on both sides. Preferably, the two gaps formed by the two damper sleeves are of different widths, with the second gap facing the closed end of the cylinder preferably being wider than the first gap facing the open end of the cylinder.

[0017] In this embodiment of the invention, the size of the pressure equalization element essentially corresponds to the size of the gap. This achieves a maximum pressure-dependent variable volume.

[0018] In a further embodiment of the invention, at least one damper sleeve is formed from two damper sub-sleeves arranged one behind the other, which have different inner contours. This results in a damper sleeve assembly made up of various damper sub-sleeves, enabling a wide variety of configurations of the damper sleeve's inner contour.

[0019] In a further development of the invention, the piston rod is designed in multiple parts. This results in simplified assembly.

[0020] In one embodiment of the invention, the inner cylinder wall has a first region that widens conically in the axial direction and a subsequent second region that narrows conically. This results in displacement-dependent damping behavior. Preferably, both pistons have an axially conically narrowing section on their outer surface facing the respective sealing disc.

[0021] In a further embodiment of the invention, the damper sleeve is made of plastic, preferably a thermoplastic material, in particular polycarbonate or polyamide. This enables cost-effective manufacturing, especially using an injection molding process.

[0022] The application of the shock absorber according to the invention is not limited to vehicles, and in particular not to two-wheeled vehicles. Rather, other fields of application also arise, such as in the area of ​​vibration damping of machines or in furniture construction. Use in the construction sector, for example for tall buildings or earthquake-resistant buildings, is also conceivable.

[0023] Other embodiments and configurations of the invention are specified in the remaining dependent claims. Exemplary embodiments are shown in the drawings and are described in detail below. The drawings show: Figure 1: Schematic representation of a shock absorber a) in a side view; b) in a transparent view; c) in longitudinal section; Figure 2: Representation of the shock absorber from Figure 1 in exploded view; Figure 3: the schematic representation of a shock absorber in a second embodiment a) in a side view; b) in a transparent view; c) in longitudinal section; Figure 4: the schematic representation of a shock absorber in a third embodiment a) in a side view; b) in a transparent view; c) in longitudinal section; Figure 5: the schematic representation of a modularly assembled damper sleeve for use in the cylinder of a shock absorber and Figure 6: the representation of the damping performance characteristics of a shock absorber within a compression-tension cycle at elevated fluid temperature with and without a pressure equalization element.

[0024] The example shown according to Figure 1The selected shock absorber comprises a cylinder 1 filled with a fluid, in this case hydraulic oil, into which a damper sleeve 2 is inserted, through which a piston rod 3 is slidably guided. A piston module 4 is arranged on the piston rod 3, which is formed from two pistons 41 connected to each other via a spacer 40. These pistons are provided with axial bores 42, and a sealing disc 43 is axially slidably mounted on the piston rod 3 at the outermost side of each piston 41. Two support discs 44 are arranged spaced apart from each other on the spacer 40 between the two pistons 41, and a pressure equalization element 5 is held between them. In the exemplary embodiment, the pressure equalization element 5 is hollow-cylindrical and made of sponge rubber.

[0025] The cylinder 1 comprises a cylinder tube 11, which is closed at both ends by a sealing and guide assembly 12. This assembly is sealed against the cylinder tube 11 by an O-ring 13 and against the radially and axially movable piston rod 3 by a hydraulic sealing ring 14. The sealing and guide assemblies 12 are each axially fixed in the cylinder tube 11 by a locking piece 15. The damper sleeve 2 is axially held in the cylinder tube 11 between the sealing and guide assemblies 12 arranged on both sides.

[0026] In the exemplary embodiment, the damper sleeve 2 is composed of three damper sleeve parts 21, 22, 23, which are made of a thermoplastic material, in this case polyamide, and whose individual inner contours combine to form the effective inner contour of the damper sleeve 2. The damping behavior of the shock absorber can be adjusted by means of the inner contour of the damper sleeve 2.

[0027] The outer diameter of the damper sleeve 2 is approximately 2 percent smaller than the inner diameter of the cylinder tube 11, thus forming a gap 16 between the cylinder tube 11 and the damper sleeve 2. The damper sleeve 2 is therefore axially fixed and floating within the cylinder tube 11.

[0028] The piston rod 3 comprises two piston rod sections 31, 32, which are screwed to the piston module 4. For this purpose, the piston module 4, in the exemplary embodiment, has axial threaded blind bores at both ends, into which a piston rod section 31, 32 with an external thread provided at each end is screwed. Alternatively, a threaded rod can be arranged, which is guided through an axial bore provided in the piston module 4 and to which the two piston rod sections 31, 32 are screwed. The two piston rod sections 31, 32 further have a reduced-diameter shoulder 33 on their side facing the piston module 4, which extends to the respective piston 41 and on which a sealing disc 43 is axially displaceably mounted.

[0029] The second piston rod section 32 has a connecting pin 34 at its end opposite the piston module 4 for connection to a connecting rod of a spring module to form a spring-damper system.

[0030] The piston module 4 consists of two pistons 41 connected to each other by a cylindrical spacer 40. The pistons 41 are essentially identical and have a cylindrical section 411 followed by a conically tapered section 412. The pistons 41 are arranged opposite each other, rotated 180 degrees, so that the tapered section 412 faces outwards. Axial bores 42 are provided in each piston 41, radially spaced from the spacer 40 and spaced regularly at intervals around their circumference.

[0031] Two support discs 44 are arranged at intervals on the spacer 40. The outer diameter of these support discs is smaller than the outer diameter of the pistons 41. A pressure equalization element 5 is held between the support discs 44. In the exemplary embodiment, the pressure equalization element 5 is hollow and cylindrical, and made of sponge rubber. The outer diameter of the pressure equalization element 5 corresponds essentially to the outer diameter of the support discs 44.

[0032] When the piston rod 3 moves in the direction of tension (tensile load), the fluid in the cylinder 1 is compressed by the first piston 41, which is located at the front in the direction of movement. This presses the sealing disc 43, located in front of the first piston 41, against the first piston 41, thereby closing the axial bores 42 in the first piston 41. The fluid is forced through the annular gap formed between the cylindrical section 411 of the first piston 41 and the inner wall of the damper sleeve 2. The flow of fluid into the annular gap is facilitated by the conical section 412, which tapers axially towards the sealing disc 43. The axially changing inner diameter of the damper sleeve 2 results in a variable width of the annular gap between the first piston 41 and the inner wall of the damper sleeve 2, thus producing variable damping.The fluid can then flow unhindered through the axial bores 42 of the second piston 41, whereby the associated sealing disc 43 is pushed away from this second piston 41 by the fluid. The second piston 41 is positioned here in the region of the maximum inner diameter of the damper sleeve 2, which is composed of the three damper sleeve parts 21, 22, 23, such that the annular gap formed between the second piston 41 and the inner wall of the damper sleeve 2 has a maximum width through which the fluid can flow. The damping effect of the shock absorber is determined by the inner contour of the damper sleeve 2 over the displacement.

[0033] When the piston rod 3 moves in the direction of pressure, the above process is reversed, whereby the fluid in the cylinder 1 is now compressed again by the piston 41 which is forward in the direction of movement and is forced through the annular gap formed between the cylindrical section 411 of this piston 41 and the inner wall of the damper sleeve 2.

[0034] As the shock absorber 1 is subjected to increasing load due to vibrations of the piston rod 3, which is equipped with the piston module 4, the fluid in the cylinder 1 heats up and expands. This expansion causes an increase in the fluid pressure, in this case, hydraulic oil. The increasing pressure of the hydraulic oil, which also acts on the pressure equalization element 5, compresses it. This increases the effective volume of the cylinder tube 11, thereby reducing the fluid pressure again.

[0035] If the fluid temperature subsequently drops again, the pressure of the fluid at the pressure equalization element 5 decreases, causing the pressure equalization element 5 to expand again. The resulting reduction in the effective volume of the cylinder tube 1 then equalizes the fluid pressure once more. In this way, the pressure equalization element 5 prevents a change in the damper performance characteristics due to a temperature increase of the fluid.

[0036] In Figure 6 The characteristic curve of the shock absorber according to the invention (measurement curve b) is compared to that of an identical shock absorber without a pressure equalization element (measurement curve a). As can be seen there, the deviation from the zero-force line caused by the increased fluid temperature in measurement curve a of the shock absorber without a pressure equalization element is eliminated in measurement curve b of the shock absorber according to the invention by the pressure equalization element.

[0037] In the shock absorber chosen as a further embodiment according to Figure 3 A damper sleeve 2' is inserted into the cylinder tube 11 of the cylinder 1. This damper sleeve is formed from two damper sleeve parts 21', 22', each having a circumferential collar 24 at its end. A hollow cylindrical pressure equalization element 5' is mounted on each of the damper sleeve parts 21', 22', its height essentially corresponding to the height of the circumferential collars 24. Recesses are provided in the end faces and in the inner, adjacent collars 24 of the adjoining damper sleeve parts 21', 22', forming a channel through which the two pressure equalization elements 5' are connected to the interior space bounded by the damper sleeve 2'. The two pressure equalization elements 5' are thus constantly supplied with fluid. The operation of the shock absorber essentially corresponds to the operation of the first embodiment described above.

[0038] If the fluid in cylinder 1 heats up, it expands, causing an increase in fluid pressure. The rising pressure of the fluid against the pressure equalization elements 5' located in the cylinder gap compresses them, thereby increasing the effective volume of the cylinder tube 11. This, in turn, reduces the fluid pressure. If the fluid temperature subsequently drops again, the pressure of the fluid against the pressure equalization elements 5' decreases, causing the pressure equalization elements 5' to expand again. This reduces the effective volume of the cylinder tube 11, thus restoring equilibrium to the fluid pressure.

[0039] To keep the width of the jacket gap accommodating the pressure equalization elements 5' small, an additional spacer 40 can be arranged between the two pistons 41 of the piston module 4, analogous to the embodiment in Figure 1 A further pressure equalization element 5 must be applied.

[0040] The shock absorber chosen as the third embodiment according to Figure 4 The assembly comprises a cylinder 6 filled with a fluid, in this case hydraulic oil, and a cylinder tube 61, which is closed at one end by a sealing and guide assembly 62. This assembly is sealed against a radially and axially movable piston rod 7 by means of a hydraulic sealing ring 63. The sealing and guide assembly 62 is axially fixed in the cylinder tube 61 by means of a closure piece 64. At its end opposite the closure piece 64, the cylinder tube 61 is closed by a plug 65. Between the closure piece 64 and the plug 65, a support ring 66 is arranged in the cylinder tube 61 as a piston guide. This support ring is provided with axial bores 67, through which the piston rod 7 is guided.

[0041] The piston rod 7 is composed of a first piston rod section 71 and a second piston rod section 72, which are screwed together and between which a first piston 73 is held. A sealing disc 75 is axially displaceable on the first piston rod section 71. An end piece 77 is screwed onto the end of the second piston rod section 72, on which another sealing disc 75 is axially displaceable. A second piston 76 is held between the second piston rod section 72 and the end piece 77, which in this embodiment has a smaller outer diameter than the first piston 73. Both pistons 73 and 76 are again provided with axial bores 74.

[0042] A split damper sleeve 8, made of a thermoplastic material, in this case polyamide, is arranged in the cylinder tube 61. It is formed from four damper sleeve parts 81, 82, 84, 85, whose individual inner contours combine to form the effective inner contour of the damper sleeve 8. A first damper sleeve assembly is positioned between the sealing and guide assembly 62 and the support ring 66. This assembly comprises two adjacent damper sleeve parts 81, 82, each of which has a circumferential collar 83 at its end. A first, hollow cylindrical pressure equalization element 5" is arranged between the collars 83 of the damper sleeve part 81, which abuts the sealing and guide assembly 62. The height of this element essentially corresponds to the height of the collar 83. A second damper sleeve assembly is formed from two further adjacent damper sleeve parts 84, 85 and is positioned between the support ring 66 and the plug 65.The damper sleeve parts 84, 85 also each have a circumferential collar 86 at their end.

[0043] A second, hollow cylindrical pressure equalization element 5‴ is arranged between the collars 86 of the damper sleeve part 85 which abuts the plug 65, the height of which essentially corresponds to the height of the collar 86. The height of the collars 86 and the pressure equalization element 5‴ is greater than the height of the collars 83 and the pressure equalization element 5‴. The space required for this is provided by the smaller outer diameter of the second piston 76 compared to the first piston 73. With the exception of the collars 83, 86, which abut the sealing and guide assembly 62 and the plug 65, all collars 83, 86 are provided with circumferential recesses, forming channels that are connected to radial bores 68 provided circumferentially in the support ring 66, which open into the axial bores 67. This ensures that the pressure equalization elements 5‴, 5‴, which in this embodiment are made of sponge rubber, are continuously supplied with hydraulic oil.

[0044] The operation of this shock absorber, in particular the pistons 73 provided with axial bores 74 in conjunction with the sealing discs 75 and with the inner contour of the damper sleeve 8, corresponds essentially to the operation of the shock absorbers described above, with the difference that the piston rod is only led out of the cylinder 6 on one side and is guided by a support ring 66 arranged in the cylinder tube 61, which acts as a piston guide.

[0045] This configuration results in a significant additional change in the effective volume of the cylinder tube 61 when the piston rod 7 with the pistons 73, 76 arranged on it moves. This leads to an underpressure or overpressure of the fluid, which in turn would impede or even block the movement of the piston rod 7. This additional volume change is compensated for by the pressure equalization elements 5‴, which are larger than those in the previous embodiments.

[0046] When the pressure of the fluid (in this case, hydraulic oil) located in the gaps formed by the damper sleeve parts 81, 85 and the cylinder tube 61 increases, due to movement of the piston rod 7 or an increase in fluid temperature, the pressure equalization elements 5" 5" are compressed. This increases the effective volume of the cylinder tube 11 accessible to the fluid, thereby reducing the fluid pressure. Conversely, when the fluid pressure at the pressure equalization elements 5" 5" decreases due to the opposite movement of the piston rod 7 or a decrease in fluid temperature, the pressure equalization elements 5" 5" expand again. This reduces the effective cylinder tube volume, thus restoring the fluid pressure to equilibrium.

Claims

1. Shock absorber, comprising a fluid-filled cylinder (1, 6) and a piston rod (3, 7) guided in it, where the piston rod (3) is inserted into or guided through the cylinder (1, 6) and applied with two pistons (41, 73, 76) at a distance from each other into which axial bores (42, 74) are applied circumferentially at a radial distance from the piston rod (3, 7), on the outside of each of which a closure disc (43, 75) is placed on the piston rod (3, 7) in an axially movable fashion to close the axial bores (42, 74) of the assigned piston (41, 73, 76), where the inner wall of the cylinder that comprises the pistons (41, 73, 76) has a diameter that is continually changing in the axial direction at least in some areas, where at least one pressure relief element (5, 5', 5", 5‴) is arranged in the cylinder (1, 6) that has a pressure-dependent variable volume and that is in contact with the fluid, characterised in that the at least one pressure relief element (5, 5', 5", 5‴) is made of elastomer foam, sponge rubber, or cellular rubber, where the inner wall of the cylinder is formed by the inner lateral surface of at least one damping sleeve (2, 8) inserted into the cylinder (1, 6), the outer diameter of which is less than the inner diameter of the cylinder (1, 6), where at least one pressure relief element (5', 5", 5‴) is arranged in the jacket gap formed between the cylinder (1, 6) and the at least one damping sleeve (2, 8), and where the jacket gap can be pressurised with the fluid through at least one penetration opening.

2. Shock absorber in accordance with claim 1, characterised in that a pressure relief element (5) is arranged between the two pistons (41), surrounding the piston rod (3) at least in some areas.

3. Shock absorber in accordance with claim 2, characterised in that at least two radially projecting support elements (44) arranged at a distance from each other are present between the pistons (41), between which at least one pressure relief element (5) is held.

4. Shock absorber in accordance with any one of the preceding claims, characterised in that the cylinder (6) is formed closed on one end, with the piston rod (7) projecting from it at the other end and with a piston guide (66) that has at least one pressure relief opening (67) being arranged between the two pistons (73, 76).

5. Shock absorber in accordance with claim 4, characterised in that at least one damping sleeve (81, 85) that forms the inner wall of the cylinder is arranged in the cylinder (6) on one side of the piston guide (66) each, through which a jacket gap each is formed in which a pressure relief element (5", 5‴) is arranged.

6. Shock absorber in accordance with claim 5, characterised in that the two jacket gaps formed by the two damping sleeves (81, 85) are formed differently wide, where the second gap that is facing the closed end of the cylinder (6) is preferably formed wider than the first gap that is facing the open end of the cylinder (6).

7. Shock absorber in accordance with any one of the preceding claims, characterised in that the size of the pressure relief element (5", 5‴) essentially corresponds to the size of the gap.

8. Shock absorber in accordance with any one of the preceding claims, characterised in that at least one damping sleeve (2, 8) is formed of at least two partial damping sleeves (21, 22, 23, 81, 82, 84, 85) that are arranged one after the other and the inner contour of which differs from each other.

9. Shock absorber in accordance with any one of the preceding claims, characterised in that the piston rod (3, 7) is formed in multiple parts.

10. Shock absorber in accordance with any one of the preceding claims, characterised in that the inner wall of the cylinder has an area that is conically widening in the axial direction in a first area and one that is conically narrowing in a subsequent second area.

11. Shock absorber in accordance with any one of the preceding claims, characterised in that the damping sleeve (2, 8) is made of plastic, preferably of a thermoplastic, in particular of polycarbonate or polyamide.

12. Shock absorber in accordance with any one of the preceding claims, characterised in that the two pistons (41, 73, 76) have a section that is conically narrowing in the axial direction on their respective outer side that faces the closure disc (43, 75).