Friction shock absorber for washing machines with free stroke and optimized operation

Abstract

The invention relates to a friction shock absorber for washing machines, consisting of a shell and a piston that slides within it, both equipped with connecting rings for attachment to the drum and frame. Inside the shell, a cap and a friction ring are provided, the latter being housed within an internally knurled ring. The knurled inner surface of this ring prevents the friction ring from sliding axially, while its outer surface features uniformly distributed projections that slide along the inner wall of the shell to ensure proper centering of the piston during movement. The friction ring extends axially beyond both sides of the knurled ring and is made of a softer plastic material, allowing the knurling to penetrate it. The shell and the cap respectively include inclined stop surfaces, which ensure progressive engagement when axial movement exceeds the free stroke.

Description

[0001] FRICTION SHOCK ABSORBER FOR WASHING MACHINES WITH FREE STROKE AND OPTIMIZED

[0002] OPERATION

[0003] The object of the present invention is a friction shock absorber for washing machines, with a free stroke and with optimized operation to ensure functional efficiency and economical manufacturing.

[0004] TECHNICAL FIELD

[0005] The use of friction shock absorbers in washing machines is known. These devices are connected to the drum and the frame of washing machines, and they serve to reduce noise and vibrations caused by the spin cycle of electric washing machines.

[0006] All known embodiments comprise a shell (or outer casing) having a substantially tubular shape and open at one end, and a piston sliding inside said shell. The shell and the piston are respectively connected to the frame and to the drum of a washing machine. The shock absorbers also comprise a cap installed at the open end of the shell, inside which the piston is inserted. The cap serves as a guide and lubrication element for the piston.

[0007] According to the prior art, the shock absorbers further comprise one or more friction rings placed between the sliding piston and the shell, configured to dampen the alternating oscillation of the piston caused by the movement of the washing machine drum relative to the frame.

[0008] Depending on the embodiment, these friction rings may be arranged inside cages sliding with respect both to the piston and to the shell— installed inside the shell but externally with respect to the piston— or they may be fixed rings inserted into dedicated seats formed in the internal wall of the shell.

[0009] PRIOR ART

[0010] Various embodiments of friction-type shock absorbers for washing machines are known in the prior art, operating in principle as described above.

[0011] In particular, regarding the operation of the friction ring, embodiments are known in which the friction ring is fixed to the piston (i.e., it slides relative to the shell) for small axial movements of the piston, and instead exerts its damping action (i.e., slides relative to the piston while remaining fixed to the shell) when the axial movement exceeds a predetermined threshold. In this way, only the larger movements of the drum— typically corresponding to the starting or ending of the spin cycle— are damped.

[0012] Document EP1286461 describes a shock absorber comprising a cage configured to hold two friction strips, one internal (in contact with the tube) and one external (in contact with the shell), and two elastic end-of-stroke elements (disc springs or compressible pads) to limit the cage's possible travel. Another embodiment is shown in EP0806514, which describes a friction shock absorber for washing machines comprising a cage equipped with a single friction strip positioned on the inside (in contact with the piston) and two end stops implemented through two helical springs. EP1584730 discloses a friction shock absorber comprising a cage with a single friction strip that may be internal (in contact with the piston) or external (in contact with the shell), two end stops made through two helical springs, and a closing cap provided with elastic fins. A variant is described in EP1637640, disclosing a shock absorber comprising a cage equipped with a single internal friction strip and two end stops— configured to limit the axial movement of the cage— formed by plastic tabs on the cap and shell. Although the end stops are rigid, they act on the friction strip; therefore, the overall end-stop function occurs elastically, exploiting the deformability of the strip itself. Document EP1754908 describes a shock absorber comprising a cage with a single friction strip formed directly in the piston. Document EP2406519 discloses an embodiment combining features of EP1637640 and EP1584730, including guides on the cage and on the shell configured to limit the relative rotation of the cage with respect to the shell.

[0013] Document EP2665854 describes a shock absorber for washing machines in which the friction element has a shape with a plurality of tips extending along the longitudinal direction of the piston toward two bearings. The friction element is enclosed inside a retaining element that protrudes axially on both sides with respect to the friction element. The diameters of the friction element and the retaining bearings are configured so that the bearings may insert inside the retaining element without interference, thereby allowing the tips of the friction element to contact the end-stop bearings. This embodiment requires a shaped friction element and two end-stop bearings, complicating manufacturing and increasing costs.

[0014] Document US5688054 describes a process for producing a sleeve-shaped support bushing comprising the following steps: forming, by molding, a thin inner sliding layer of a polymeric material without abrasive fillers on a core; producing a longitudinal gap on the outer surface of the sliding layer from one end to the other; and coating the inner sliding layer with an external support made of another polymeric material, joining the inner layer to the outer support by filling the gap. This method therefore describes a process enabling the simple, economical, and non-polluting manufacturing of a sliding bearing with a plastic sliding layer.

[0015] Document US2031349089 describes a friction shock absorber for damping vibrations generated by a drum of a laundry treatment machine, comprising: a hollow piston body; a piston rod configured to move telescopically along a central longitudinal axis of the hollow piston body; a friction element made of elastic material interposed between the hollow piston body and the piston rod, where friction is generated when the piston rod moves relative to the hollow piston body; fastening portions at the free ends of the piston rod and hollow piston body to connect the friction shock absorber to the laundry treatment machine; and at least one stop portion interposed between the hollow piston body and the piston rod to limit movement of the friction element in the direction of the central longitudinal axis. All other known embodiments are nevertheless limited because, alternatively: they require more than one friction strip (or ring); they require a cage made of more than one piece; they use the cage (which is a rigid element) as the end stop; they have a free axial stroke that is not adjustable, preventing adaptation of the piston to different washing machine models.

[0016] PURPOSE OF THE INVENTION

[0017] The purpose of the invention is therefore to provide a friction shock absorber for horizontal-axis washing machines that overcomes the limitations of the prior art, and in particular: that is economical to manufacture, not requiring multiple friction rings or multi-piece cages; that uses a non-rigid element (the friction strip or ring) as the end stop, with a simple shape and easy application; that has an adjustable free axial stroke, allowing use in different washing machine models; and that applies the damping force progressively rather than immediately at maximum value.

[0018] BRIEF DESCRIPTION

[0019] The invention concerns a friction shock absorber for washing machines, in which a piston (1) slides inside a shell (2) and cooperates with a friction system designed to ensure stable and controlled damping. Inside the shell is an internally knurled ring (5) that houses a friction ring (4), with the knurled surface preventing any axial sliding of the friction ring relative to the internally knurled ring. The knurled ring is provided on its outer surface with uniformly distributed projections (52), which slide along the inner surface of the shell (2) to keep the piston centered during its axial movement. The friction ring (4) protrudes axially on both sides of the internally knurled ring (5), improving its frictional engagement. The knurled ring is made of a rigid plastic material, while the friction ring is formed from a less rigid plastic so that the knurling penetrates into it, ensuring stable coupling. The shell (2) further includes an inclined internal abutment surface (24), and the cap (3) features a correspondingly inclined stop surface (31), contributing to the correct positioning and operation of the damping assembly. DETAILED DESCRIPTION

[0020] A detailed description of preferred embodiments of the invention is provided with reference to figures

[0021] 1 to 14.

[0022] Figure 1 shows an external view of the piston according to the invention, partially sectioned in figure

[0023] 2 and in cross-section in figure 3. Figure 4 shows a sectional view of an embodiment including an endstop adjuster; figure 5 shows an exploded lateral view of all components; figure 6 shows an isometric view of the shock absorber according to the invention, partially sectioned in figures 7 and 8 in the embodiment with end-stop adjuster, and in figure 9 in the embodiment without end-stop adjuster.

[0024] Figures 10 and 11 show two views where the end-stop adjuster is also sectioned; figure 12 shows an exploded isometric sectional view of the device; figure 13 an exploded isometric view; and figure 14 a sectional detail.

[0025] As shown in figure 1, the device comprises a shell (2) within which a piston (1) is slideable. Both the shell (2) and the piston (1) are provided with connecting rings (21, 11) for attachment to the frame and drum of a washing machine, particularly a horizontal-axis washing machine.

[0026] As visible for example in figure 2, the shell (2) comprises— axially starting from the side where the piston (1) is inserted— a first portion (22) housing the cap (3) and the friction ring (4) with its corresponding ring (5), and a second portion (23) in which the piston (1) slides.

[0027] The shell, piston, and cap may be manufactured according to any embodiment known in the prior art without departing from the purpose of the invention.

[0028] Conveniently, the device according to the invention is characterized in that the friction ring (4) protrudes axially on both sides from the ring (5), and in that the ring (5) is internally knurled so as to prevent axial sliding of the friction ring (4). For the sake of clarity, the ring (5) will hereinafter be referred to as the knurled ring (5).

[0029] Figure 12 shows the knurling (51) on the inner surface of the knurled ring (5), as well as the projections (52) on its outer surface configured to slide on the inner surface of the shell (2). The knurling penetrates, once the device is assembled, into the outer surface of the friction ring (4).

[0030] The presence of the projections (52) on the outer surface of the knurled ring (5) provides a centering function for the friction ring (4) and therefore for the piston (1) during axial sliding. Their reduced surface area also limits friction so that during the free stroke phase of the piston there is no substantial energy dissipation.

[0031] As apparent from the drawings, these projections (52) are uniformly distributed along the outer surface and are configured to slide on the internal surface of the shell (2) to provide centering of the piston during its axial motion. Preferably, these projections (52) are six in number.

[0032] As shown in figure 16, the outer end of said projections (52) is preferably curved and convex to limit the contact surface between the projections (52) and the interior of the shell, in order to reduce frictional force.

[0033] As immediately understood from the various sectional views, when the piston (1) moves axially relative to the shell (2) over small excursions, the friction ring (4) does not contact either the cap (3) or the abutment surface (24) in the shell (2), and therefore exerts no friction force.

[0034] For larger axial movements, the friction ring (4) comes into contact with the cap (3) on one side and with the internal abutment surface (24) of the shell (2) on the other, thereby exerting a frictional force relative to the piston (1).

[0035] Preferably, the friction ring is made of polyurethane (PU), and the knurled ring (5) is made of polyoxymethylene (POM) or other rigid plastic. In this way, the knurling of the knurled ring (5) penetrates the friction ring (4), which is made of a softer material.

[0036] It should therefore be noted that— since the end-stop function is performed by the friction ring (4) and not by the knurled ring (5)— the end stop is made of soft material without the need for additional polyurethane elements, as in some prior-art embodiments.

[0037] The friction ring (4) is manufactured by using a strip of polyurethane wound to form a ring. Therefore, the terms "friction ring" and "strip" are interchangeable in this patent.

[0038] Regarding materials, without limiting the invention, the shell (2) may conveniently be made of polypropylene, the cap (3) of polypropylene or polyoxymethylene, and the sliding portion of the piston (1) inside the shell (2) is preferably made of a metal sheet.

[0039] Having explained the construction of the knurled ring (5) and strip (4), the advantages become clear: the functions of cage, friction ring, and end stop are all achieved using only two components, which are economically produced and have no difficult geometries.

[0040] Regarding the abutment surface (24) in the shell (2), it is noted that— preferably but not necessarily— it is not orthogonal to the axis of the shell, but inclined with respect to it. In this way, the strip contacts the abutment surface (24) starting from its outer edge, and the force applied gradually increases from zero to the maximum value, unlike what would occur with a stop orthogonal to the shell's axis.

[0041] Preferably but not restrictively, the abutment surface (24) is inclined at an angle between 30° and 60° with respect to the direction orthogonal to the sliding direction, and more preferably between 40° and 50°. Similarly, the stop surface (31) on the cap (3) is preferably inclined relative to the axis of the shell to obtain the same technical effect.

[0042] As shown in figure 4, in a preferred embodiment the device comprises an end-stop adjuster (6) insertable inside the shell (2) to limit the free stroke of the strip (4).

[0043] Conveniently, the end-stop adjuster (6) is ring-shaped (allowing the piston (1) to slide inside it), is configured to abut against the end abutment surface (24) of the shell (2), and features on the side facing the cap (3) an inclined abutment surface (64) as described above for the shell's abutment surface (24).

[0044] In this way, by appropriately varying the thickness of the end-stop adjuster (6)— or by inserting more than one adjuster— the free stroke of the strip (4) can be varied to adapt the shell (2) to different washing machine models without requiring additional modifications.

Claims

CLAIMS1. Friction shock absorber for washing machines comprising a shell (2), a piston (1) sliding inside the shell, a cap (3), a friction ring (4), said shell (2) and said piston (1) being provided with connecting rings (21, 11) for connection to the frame and to the drum of a washing machine, characterized in that the device further comprises an internally knurled ring (5) inside which said friction ring (4) is housed, so that the knurled surface prevents axial sliding of said friction ring (4) relative to said internally knurled ring, and in that said knurled ring (5) comprises, on its external surface, a plurality of projections (52), uniformly distributed along said external surface and configured to slide on the inner surface of said shell (2) so as to perform a centering function for the piston during axial sliding movement, and in that said friction ring (4) protrudes axially on both sides with respect to said internally knurled ring (5), and in that said friction ring (4) is made of a plastic material less rigid than said knurled ring (5), so that the knurling of said knurled ring (5) penetrates into said friction ring (4), and in that said shell (2) comprises an internal abutment surface (24) inclined with respect to the direction orthogonal to the axis of said shell, and said cap (3) comprises a stop surface (31) inclined with respect to the axis of said shell.

2. Friction shock absorber for washing machines according to claim 1 characterized in that saidshell (2) comprises a first portion (22) in which said cap (3) and said friction ring (4) with corresponding knurled ring (5) are housed, and a second portion (23) in which the piston (1) slides.

3. Friction shock absorber for washing machines according to claim 1 or 2 characterized in that said internally knurled ring (5) comprises a plurality of projections (52) on its outer surface configured to slide on the inner surface of the shell (2).

4. Friction shock absorber for washing machines according to any of the preceding claims characterized in that said friction ring (4) is made of polyurethane (PU), and said knurled ring (5) is made of polyoxymethylene (POM) or another rigid plastic material.

5. Friction shock absorber for washing machines according to any of the preceding claims characterized in that said friction ring (4) is made using a strip of polyurethane wound to form a ring-shaped configuration.

6. Friction shock absorber for washing machines according to any of the preceding claims characterized in that said shell (2) is made of polypropylene, said cap (3) is made of polypropylene or polyoxymethylene, and said piston (1) — at least for the portion sliding inside the shell (2) — is made of a metal sheet.

7. Friction shock absorber for washing machines according to claim 1 characterized in that said abutment surface (24) of the shell (2) and said stop surface (31) of the cap (3) are inclined at an angle between 30° and 60° with respect to the direction orthogonal to the axis of the shell.

8. Friction shock absorber for washing machines according to any of the preceding claims further comprising at least one end-stop adjuster (6), insertable inside the shell (2) in order to limit the free stroke of said friction ring (4).

9. Friction shock absorber for washing machines according to any of the preceding claims characterized in that said end-stop adjuster (6) is ring-shaped, so that the piston (1) can slide inside it, and is configured to abut against said end-stroke abutment surface (24) of the shell (2), and comprises, on the side facing the cap (3), an inclined stop surface (64) corresponding to said abutment surface (24).

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