Field of the invention

The present disclosure relates to a laundry washing machine comprising a rotatable drum, and a suspension arrangement devised to carry the drum in relation to a base structure, located under the washing machine and on which the washing machine rests, wherein the suspension arrangement comprises at least one piston damper.

Technical background

Such washing machines are widely used, for instance as washing machines suitable for professional use. One problem with such machines is how to reduce vibrations and transmission of force to the floor or the like on which the machine rests.

Summary

One object of the present disclosure is therefore to provide a washing machine with reduced vibrations and transmission of force to the floor caused by movements of the drum inside the machine. This object is achieved by means of a machine as defined in claim 1. More specifically, in a machine of the initially mentioned kind there is provided a speed sensing arrangement, determining the rotating speed of the drum, and the piston damper comprises a clamp arrangement. Thanks to the clamp arrangement, the piston damper is switchable between a high-friction and a low- friction state, based on the determined rotating speed, when the rotating speed increases, reaching a threshold value. Thereby, the dynamic properties of the suspension arrangement can be adapted such that an increased friction is used at low rotation speeds, such as during washing and rinsing, while a lower friction is used at high speeds, typically during extraction of water, thereby providing decreased vibrations and transmission of forces.

The piston damper may comprise a cylinder, a piston, moveable in the cylinder, and a rod, attached to the piston and extending out of the cylinder, and the clamp arrangement may be devised to selectively clasp or release the rod to increase or decrease, respectively, the friction of the piston damper.

The clamp arrangement may comprise a first portion attached to the cylinder and a second portion connected, at a proximal end, to the first portion by means of a hinge and may be pivotable in relation to the first part to selectively clasp or release the rod. A distal end of the second portion may be moved by means of an actuator to selectively clasp or release the rod, and typically the actuator may a solenoid.

In a typical example, four such suspension arrangements are used, one at each corner of the washing machine.

The determining of the rotating speed of the drum may be based on a washing schedule or may be based on one or more accelerometers located on the drum, or on currents driving a motor of the drum.

The present disclosure also considers a piston damper for a laundry washing machine comprising a cylinder, a piston, moveable in the cylinder, and a rod, attached to the piston and extending out of the cylinder, where a clamp arrangement is devised to selectively clasp or release the rod to increase or decrease, respectively, the friction of the piston damper.

The clamp arrangement may comprise a first portion, attached to the cylinder and a second portion connected, at a proximal end, to the first portion by means of a hinge and being pivotable in relation to the first part to selectively clasp or release the rod.

A distal end of the second portion may be moved by means of an actuator to selectively clasp or release the rod. Typically, the actuator may be a solenoid. A setting screw is provided that determine a maximum friction of the piston.

Brief description of the drawings Fig 1 shows a perspective view of a washing machine.

Fig 2 shows a perspective view of suspension arrangement carrying a drum.

Fig 3 illustrates schematically a suspension arrangement and enlarged a conventional damper thereof.

Fig 4 shows a perspective view of semi-active damper according to the present disclosure.

Fig 5A and 5B show the clamp parts for the damper of fig 4.

Figs 6 and 7 show the semi-active damper in its two states.

Fig 8 illustrates transmission of forces to ground for different scenarios. Detailed description

The present disclosure relates generally to a washing machine 1 , an example of which is shown in fig 1. The washing machine comprises an outer housing 3 and rests on a base structure 5, which is typically a floor, but in principle could be a rack or another machine, for instance. At a front side 7 of the washing machine, there is located a door 9 through which the interior of a drum is accessible. There also exist machines where laundry is inserted from the top of the machine, and the present disclosure is equally relevant to such machines.

Fig 2 shows a suspension arrangement carrying a rotatable drum 11 inside the housing 3 of fig 1. The rotatable drum 11 is located inside a typically cylindrical drum housing 13, which is carried by a drum frame 15, which in turn is carried by a suspension arrangement 17, 19, comprising dampers 17 and springs 19 connecting the drum frame 15 to a bottom part 21 of the machine that rests on the base structure/floor 5. Typically, one damper/spring 17/19 combination is used in each corner, the machine having a rectangular floor layout.

Illustrated in fig 2 is a transport lock plate 23 that rigidly connects the drum frame 15 to the bottom part 21 until the machine 1 is installed in a location where the machine is to be used. Then, the transport lock plate 23 is removed such that the drum 11 and the drum frame 15 are carried by the dampers 17 and springs 19, generally forming a parallel spring-damper mass system as is schematically illustrated in fig 3. This is done to minimize ground force transmission from the drum rotating with laundry therein, in order to avoid e.g. the machine 1 moving on the floor and making exces sive noise. The illustrated enlarged portion of fig 3 shows the damper 17, which very schematically has first and second anchor holes 27, one at the end of a cylinder 29 and one at the end of a rod 31 , extending out of the cylinder 29. The rod 31 is connected to a piston 20 located inside the cylinder and being provided with orifices. The rod 31 is capable of moving the piston inside the cylinder 29 thereby displacing a fluid inside the cylinder through the orifices of the piston as is well known per se. Other ways of producing such friction in a damper exist.

The present disclosure is related to an arrangement for reducing washing machine drum oscillations. In a washing machine 1 of the above described kind, non-uniform mass distribution of laundry inside the rotating drum generates a centrifugal force acting on the system, which produces drum oscillations and transmission of dynamic forces to the base structure on which the machine rests.

According to the present disclosure such oscillations and transmission of forces are reduced by use of semi-active dampers an example of which will now be shown with reference to fig 4, which shows a perspective view of semi-active damper according to the present disclosure.

By a semi-active damper is here meant a damper capable of being switched between two values of damping in contrast to the passive damper schematically illustrated in fig 3.

With reference to fig 4, the semi-active damper 33 comprises first and second anchor holes 27, a cylinder 29 and o a rod 31 , extending out of the cylinder 29, as in a passive damper. In addition to this, the semi-active damper comprises a clamp arrangement 35, 37, which is devised to selectively increase or decrease the damper’s friction.

The clamp arrangement illustrated in fig 4 comprises a first, fixed portion 35, which is attached to the cylinder 29 of the damper, typically integrally formed therewith as shown in fig 5A. The clamp arrangement further comprises a second portion 37, also shown in fig 5B. The first and second clamp portion 35, 37 comprise hinge features 41 that together with a protruding pin shown in fig 4 form a hinge 39.

A fixed, L-shaped bracket 43 is attached to the first clamp portion 35, screw holes 45 may be provided in the clamp portion 35 to facilitate this, as shown in fig 5A.

Similarly, screw holes may be provided also in the second clamp portion 37, and as shown in fig 4 a bracket 47 may be attached thereto, which is movable in relation to the fixed bracket 43, thanks to the second clamp portion 37, which is pivotably connected, at a proximal end, to the first portion 35 by means of a hinge 39.

Typically, the first and second clamp portions 35, 37 may be made in plastic or cast metal, while the brackets 43, 47 may be made of sheet metal.

The first and second clamp portions 35, 37 are thus moveable in relation to each other by moving the moveable bracket 47 in relation to the fixed bracket 43, and are capable of clasping the rod 31 , thereby significantly increasing the friction caused when moving the rod 31 linearly in relation to the cylinder 29. As illustrated in figs 5A and 5B, inserts 49 may be provided at the interior sides of the clamp portions 35, 37 to provide surfaces with properties suitable for increasing the friction against the damper cylinder rod 31.

The distal end of the second clamp portion 37 may be moved by means of an actuator 51 to selectively clasp or release the rod 31. As illustrated in fig 4, the actuator 51 may be attached to the fixed, L-shaped bracket 43, and a piston (53, of. figs 6-7) of the actuator may be connected to the moveable bracket 47 close to the end most distant from the hinge 39. Typically, the actuator may be a solenoid, although other linear actuators are conceivable.

Figs 6 and 7 illustrate schematically the operation of the semi-active damper in its two states. In fig 6, the damper is in its closed position with the clamp portions 35, 37 clasping the damper rod 31. The tightness of the clasping may be determined by means of a screw 55, which sets a minimum distance in between the brackets 43,

47. In this state, the solenoid 51 pulls the solenoid piston 53 to its most retracted position, thereby achieving the clasping of the rod 31. The solenoid 51 (or other actuator) is controlled by a control unit 57, which is connected to a speed sensing arrangement 59. The speed sensing arrangement 59 determines the rotating speed of the washing machine drum. When the rotating speed increases, reaching a threshold value, the control unit activates the solenoid 51 to force the solenoid piston 53 into an extended position, as shown in fig 7, thereby releasing the clasping of the rod 31. The speed sensing arrangement 59 may comprise an rpm meter connected to the drum or accelerometers on the drum. As a further alternative, the speed may be determined simply by determining which phase of the washing cycle presently is processed, e.g. rinsing or extracting, which implies different drum speeds.

The mechanism of the semi-active dampers is used to optimize the behavior of the washing machine over a broad range of drum rotation speeds. At speeds close to the drum’s resonance speed, high friction is preferable, as this dissipates a lot of the vibration energy. The drum’s resonance speed depends on the weight and the distribution of the laundry in the drum and is therefore not predetermined, but usually is close to the few tens of revolutions per minute that are used during the washing and rinsing phases. However, during the extraction phase, where the drum speed is much higher, lower friction is preferred as this prevents transmission of forces to the ground at higher vibration frequencies. Fig 8 illustrates transmission of forces to ground for different scenarios. Plot 61 shows the result where no friction at all is applied e.g. where the damper is removed. Relatively high forces are transmitted at low frequencies, whereas the damping functions relatively well at higher frequencies. On the other hand, a high friction damper gives as illustrated by plot 63 functions relatively well at lower frequencies, while at higher frequencies relatively high forces are transmitted as the damper functions as link between the drum and the base structure.

By switching between high and low friction damping at a suitable rotation speed, a lower possible transmission of forces can be achieved over the entire spectrum of rotation speeds as illustrated with plot 65, which illustrates a characteristic where dampers according to the present disclosure are used. The above-described clasping of the damper rods is thus released at a threshold frequency located above the resonant frequency, such that reduced overall maximum transmission of forces is achieved. The present disclosure is not restricted to the above-described embodiment and may be varied and altered in different ways within the scope of the appended claims.