US 3389881 A
Description (OCR text may contain errors)
RESILIENT SUPPORTS FOR ROTATING MACHINE PARTS Filed July 12, 1966 4 Sheets-Sheet 1 INVENTOR. JAN STELWA GEN BY M AGE.
June 25, 1968 J. STELWAGEN 3,389,881
RESILIENT SUPPORTS FOR ROTATING MACHINE PARTS Filed July 12, 1966 4 Sheets-Sheet 2 INVENTOR. JAN STELWAGEN BY M AGENT June 25, 1968 J. STELWAGEN 3,389,881
RESILIENT SUPPORTS FOR ROTATING MACHINE PARTS Filed July 12, 1966 beets-Sheet 3 n 23 FIG. 30 FIG. 3b
FIG.6 F157 INVENTOR. JAN STELWAGEN June 25, 1968 J. STELWAGEN 3,389,881
RESILIENT SUPPORTS FOR ROTATING MACHINE PARTS Filed July 12, 1966 4 Sheets-Sheet 4 I 5 108 T I 1 1; 105
INVENTOR. JAN STELWAGEN BY 2M A7.
United States Patent 3,389,881 RESILIENT SUPPORTS FOR ROTATING MACHINE PARTS Jan Stelwagen, Emmasingel, Eindhoven, Netherlands, as-
signor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed July 12, 1966, Ser. No. 564,616 Claims priority, application Netherlands, July 17, 1965, 6509288 1 Claim. (Cl. 248-18) ABSTRACT OF THE DISCLOSURE A suspension system for rotatable drums of the type utilized in domestic washing/drying apparatus. A rotatable drum is suspended in a rigid framework by a plurality of spring and damping elements which co-act to define an elastic system having an elastic center positioned along the central axis of the drum and particularly at the center of mass of the total rotating system. The tension of springs which support the drum can be regulated thus permitting adjustment of the position of the elastic center of the elastic system.
The invention relates to a support for resiliently mounting a frame part, which supports the bearings of a rotatable component, for example, a drum of a device for Washing or spin-drying clothes with respect to a fixed frame part. The support comprises an elastic system consisting of a number of resilient elements, the elastic system having an elastic centre.
In rotatable components as meant here, difficulties are often encountered when, because a part of the mass thereof becomes located eccentrically with respect to the axis of rotation as a result of the type of the construction or the operating conditions, or forces and moments occur by other causes. For example, magnetic or electrcmagnet'c forces, which, on rotation, rapidly vary their direction are transmitted to the frame of the machine through the bearings. These periodic loads may easily result in unacceptable situations, both with regard to the use and to the life of the structure, particularly when the number of revolutions per minute is high.
In order to hold the forces and moments occurring within permissible limits, a part of the frame supporting the bearings of the rotatable component is resiliently secured in a given manner to the remaining part of the frame. As a result of this, the rotating part, and the part supporting the bearings, are enabled to collectively approach a main axis of inertia as the axis of rotation.
The resilient support of the part of the frame supporting the rotatable component must satisfy a number of conditions. First of all said support must be capable of bearing the static load as a result of the constructions own weight. In addition, the support must give the system low critical natural frequencies both for the translation vibrations as a result of periodic forces acting in the direction of the axis of rotation and in directions at right angles thereto, and for the rotation vibrations as a result of the periodic moments operating in the same directions. Finally, the system must be dynamically stable at the operating speed of rotation. A difficulty in this connection is that vibrations occurring in or about a given direction result in vibrations in or about the other directions so that the total vibration picture becomes very complicated.
The requirements mentioned here determine the shape, the proportions, the type and the position of the resilient elements of the resilient support.
According to the invention, a rotatable drum for a washing/drying machine is suspended in a rigid frame- 3,389,881 Patented June 25, 1968 ice I work. The suspension assembly includes a plurality of spring and damping elements which support the drum in an elastic system having an elastic center along the central axis of the drum, preferably at the center of mass of the drum. In one embodiment of the invention a drum having a vertically positioned centroidal axis is disposed within a rigid frame. A shaft aligned with the centroidal axis of the drum interconnects the drum with a motor. A resilient element provides an elastic attachment between the motor and the frame. A pair of damping elements interconnect the shaft to the frame.
The elastic centre may be defined as the point of intersection of a system of elastic principal axes. The principal axes comprise a system of three axes which extend mutually at right angles, each having the prop erty that a force acting along an axis causes only a translation of the resiliently supported components in the direction of that axis and a torque acting about the direction of the axis causes only an angular movement about the direction of that axis.
When this condition is fulfilled a favourable condition is reached for the elastic system in that the degrees of freedom of vibration for translation and angular displacement of the resiliently supported frame part are separated from one another, so that the vibration picture is simplified and the behaviour of the system can be better controlled.
A further improvement is achieved by a decrease of the number of degrees of freedom. If the system is constructed so that an elastic principal axis thereof coincides at least approximately with a principal axis of inertia of the resiliently supported frame part.
It has been stated above for the elastic centre and for the centre of mass that these must meet at least approximately certain requirements, notably, that the said points must coincide at least approximately. It is clear that the closer the points approach the desired condition, the more favourable is the dynamic behaviour of the resiliently supported frame part.
However, in practice it is very difficult to actually reach this most desired situation. In connection herewith, according to the invention the practical requirement is imposed that the elastic centre and the said centre of mass must be located within the area of a cross-sectional plane of the rotatable component determined by the circumference of the said component at right angles to the centre line of its bearings.
In this connection it is of advantage when the elastic system is constructed so that the elastic centre thereof is adjustable. According to the invention this can be reached by one or two or by a combination of two measures, namely in that the spring tension of at least one of the resilient elements of the resilient support is controllable in such manner that the elastic centre thereof can be positioned at least approximately in the centre of mass of the resiliently supported frame part, and in that at least one point of action of at least one of the resilient elements of the resilient support is controllable in such manner that the elastic centre of the elastic system can be arranged at least approximately in the centre of mass of the resiliently supported frame part. In this manner, either the value or the directionor both-of the force which is exercised by at least one of the resilient elements can be controlled.
What has been described above for the elastic properties of the elastic system can be applied in an analogous manner to the properties thereof which determine the damping of the periodic movements of the resiliently supported frame part. The elastic system may also be considered to be a damping system, and a damping centre and damping principal axes may be defined in a similar manner. So everywhere where an elastic centre and elastic principal axes are mentioned, the expressions may be replaced by damping centre and damping principal axes respectively to obtain similar advantages and to yield analogous effects.
Other advantages of the invention will be apparent from the following description of a few embodiments with reference to the drawings, in which FIGURE 1 is a rear view of a domestic clothes washer and spin-drying machine according to the invention after removing the rear wall.
FIGURE 2 is a side elevation of the same machine after removing a side wall,
FIGURE 3a and 31) show the connection of one of the resilient elements to the tub in front and side view respectively.
FIGURE 4 shows a connectionof a resilient element the resilience of which can be controlled.
FIGURE 5 shows a connection of a resilient element of which a point of action can be displaced.
FIGURE 6 is a diagrammatic cross-sectional View at '1 right angles to the axis of the same machine in another embodiment.
FIGURE 7 is a diagrammatic cross-sectional view in the direction of the axis of rotation of still another embodiment of the machine of this type,
FIGURE 8 is a vertical cross-sectional View of a domestic spin-drying machine for washing which has a vertical axis of rotation, and
FIGURE 9 is a horizontal cross-sectional view taken on the line A-A of the machine shown in FIGURE 8.
The domestic clothes washing and spin-drying machine shown in FIGURES 1 and 2 comprises a frame 1 which consists of a bottom plate and a top plate and four upright side walls which usually are manufactured from sheet steel, if required reinforced by means of ribs, corner pieces, and so on. In this frame is arranged a tub 2, likewise of sheet steel, for containing the wash-liquid. This tub comprises the bearings 3 for the shaft 4 of a cylindrical drum 5 in which the clothes are to be washed. The drum is preferably manufactured from perforated stainless steel plate. The centre line of the bearings of the shaft of the drum is denoted by 6. The shaft of the drum comprises a pulley 7 which is driven by a motor 9 through a belt 8 and a pulley 10 secured to the shaft of the motor.
The motor 9 is secured to the tub 2. The motor with the transmission mechanism coupled thereto is constructed for driving the drum at a speed of approximately 50 revolutions per minute during washing, that is when the drum contains clothes and the tub is filled with washing liquid. The drum is driven at a speed which exceeds 800 revolutions per minute and preferably is 1200 to 1500 revolutions per minute during spin-drying, when the tub is empty. This speed is required for removing the sufficient liquid out of the clothes. In this embodiment the washing drum has an outside diameter of approximately 50 cms.
At its top side the tub 2 comprises an opening 11 for loading the washing. The drum 5 has a corresponding opening in its cylinder surface which opening can be closed by a cover (not shown). The opening 11 in the tub adjoins an opening 12 in the frame which can be closed by a cover 13. Between the tub 2 and the frame 1 a sleeve 14 of flexible material, for example, rubber, is provided around the opening 12 for sealing purposes.
The tub 2 to which the motor 9 is secured and in which the drum 5 is journalled is resiliently connected to the frame 1 in such manner that the forces and moments produced by the eccentric load as a result of the presence of the washing in the drum 5 during operation are not transmitted, or are transmitted only to a very small extent, to the frame 1. This resilient connection includes a number of resilient elements, namely four helical springs 15 and four rubber rings 16. The elements 15 and 16 together constitute an elastic system and are chosen to be so that the elastic centre of this system theoretically coincides with the centre of mass of the resiliently supported part of the machine, namely the tub 2 with the drum 5 journalled therein and the parts secured thereto, for example, the motor and other components which are not shown.
One of the elastic principal axes of the system coincides with a principal axis of inertia of the resiliently supported part. The calculation methods necessary to obtain this are considered to be known to those skilled in the art so that these need no further explanation here.
The upper ends 17 of the helical springs 15 are secured to a metal board 18 rigidly secured to the frame 1 by means of screw-threaded members 35 provided with nuts 27; the lower ends of saidmembers are provided with eyelets 36, through which the ends 17 of the springs are threaded (FIGURE 4).
Their lower ends 19 are formed into hooks which are threaded in strips 20 welded to the tub 2.
The upper ends of the rubber rings 16 which have the shape of an elongated loop are slid onto pins 21 secured to the metal strips 24 connected to the tub 2 in the manner as shown in FIGURE 3. Their lower ends are slid in a corresponding manner onto pins 22 secured to a board 25 which forms a part of the frame 1.
The frame 1 is placed on casters 26 which is possible by using the invention, since no or substantially no periodic inertia forces act upon the frame.
The springs 15 are arranged approximately in a vertical position. These springs carry the weight of the resiliently supported parts. These springs are chosen to be as slack as possible so as to give the system the lowest possible natural frequencies. In this case a limit is imposed upon the natural frequencies to be reached by the static elongation of the springs. The additional elongation of the springs when the tub is filled with washing liquid and the drum with washing may in general not exceed a few centimetres. This means that a natural frequency in a vertical direction which is smaller than approximately 2 cycles per second, can substantially not be reached. In a horizontal direction, however, the natural frequency in this arrangement need not be higher than approximately 1 cycle/ sec.
A system can be obtained, the natural frequencies of which are different in two mutually perpendicular directions which facilitates the passing of those frequencies and restricts the motor torque necessary to rapidly pass the said frequencies. The rubber rings 16 in general do not contribute to carrying the weight of any structural component. These rings which are arranged at an angle of approximately first of all have the function of causing the elastic centre of the resilient support to coincide with the centre of mass of the resiliently supported part and, secondly, they serve for damping the vibrations which occur during passing a critical speed. They are preferably manufactured from an elastomer, for example, butyl rubber, which has damping properties which are independent of the vibration frequency.
As a result of this it is prevented that the said elements absorb too much energy at high frequencies, which would require an unnecessarily large motor power and would raise the temperature of the elements themselves too much.
The tension of the springs 15 can be controlled in a simple manner by displacing the nuts 27 as shown in FIGURE 4. The stress of the rings 16 can be controlled in a simple manner by displacing the pins 21 in the slots 37 of the strips 24 as shown in FIGURE 3. The connection point of the rings 15 to the tub 2 can be made adjustable in the manner as shown in FIGURE 5. For this purpose, the tub 2 is provided with corner pieces 28, comprising slots 29 through which bolts can be inserted with which the strips 24 are secured to the corner pieces 28. These measures enable the elastic centre of the elastic system to approach the centre of mass of the resiliently supported parts as closely as possible.
In this embodiment it can be ensured that the abovementioned coinciding elastic centre and the centre of mass lie in the plane which is denoted by 31 in FIG. 2, which is a plane which extends at right angles to the centre line 6 of the bearings of the drum and which divides the drum into two equal parts. It can likewise be ensured that the elastic main axes and the main axes of inertia coincide two by two. The modes of calculation to obtain the end in view are likewise considered known to those skilled in the art.
Instead of the vertically arranged helical springs it is of course also possible to use springs which are arranged at an angle as diagrammatically shown in FIG URE 6 (springs 32), while instead of the rubber rings 16 steel helical springs may be used, for example, the springs 33 in FIGURE 6. In addition it is possible to arrange resilient elements in the elongation of the centre line 6, for example, the springs 34 shown in FIGURE 7. In that case springs are preferably used which have a great rigidity in the direction of the centre line 6 and possibly a negative rigidity in the directions at right angles thereto, as a result of axial pre-stress or torsional pre-stress. Both steel springs and rubber rings may be used for this purpose. This construction has particular advantages, when the drum 5 has a large length in relation to its diameter and consequently a proportionately large moment of unbalance in a direction at right angles to the shaft is to be expected as a result of unequal distribution of the washing over the longitudinal direction.
The pre-stress and the resulting negative rigidity of one or both elements 34 located in the direction of the centre line 6 further has the advantage that this negative rigidity can compensate for the positive rigidity of the springs 32 and 33 so that a system can be obtained which has low critical natural frequencies at a small sag of the supporting springs as a result of the static load. In this connection it is still of advantage when the said pre-stress is made adjustable.
The invention may likewise be used advantageously in machines, in which the axis of rotation of the components to be rotated is vertical. An example hereof is a domestic spin-drier for removing liquid from washing. For a satisfactory operation of such a machine the drum must preferably have a speed of at least 3000 rpm. when the drum has an average diameter of at least cms. An example of such a spin-drying machine using the invention is diagrammatically shown in FIGURE 8 as a longitudinal cross-sectional view, and in FIGURE 9 which is a cross-sectional view taken on the line AA in FIGURE 8. The machine comprises a cylindrical housing 101 preferably manufactured from sheet steel having a steel bottom 102 and at its top a cover 103. Said housing comprises a drum 104 having a vertical axis of rotation, which drum is preferably manufactured from perforated stainless steel plate. Said drum is driven by a motor 105 arranged below said drum through the motor shaft 106 which is directly connected to the drum 104. The motor shaft 106 and the drum 104 have a common centre line 107. The motor shaft is journalled in ball-bearings 108 which are arranged in a bushing 109 rigidly secured to the housing of the motor. The motor 105 with the drum 104 secured thereto are resiliently supported in the vertical direction by a rubber spring 110 which engages the bottom 102 of the housing and which is arranged in the centre line 107 and on which the motor housing bears, and in the horizontal direction by three identical rubber rings 111 having the shape of a loop which are arranged at regular mutual angular distances at one end to the housing 101 and at the other end to the bearing bushing 109.
Instead of rubber rings 111 steel helical springs may also be used. The springs 110 and rings 111 together constitute an elastic support for the motor and the drum 104 which are combined to form one unit. These springs are chosen and arranged so that the elastic centre of the system and the centre of mass of the said unit coincide. To reach this in practice the points of connection of the rings 111 may again be made adjustable in an analogous manner to that described in the first embodiment, but which is not shown again.
The rubber spring which in this example is the resilient element which for the greater part supports the weight of the supported component in the static condition, may have a rectangular or circular cross-section. On its upper and lower sides it is provided with steel plates 112 secured thereto by vulcanisation for securing purposes at one end to the bottom 102 and at the other to the housing of the motor 105. The spring 110 which for the same reasons as described for the first embodiment is again manufactured preferably from butyl rubber is proportioned so and the rings 111 are chosen and arranged so that the resiliently supported system has a natural frequency in the vertical direction of approximately and preferably not more than 10 cycles per second, while in two mutually perpendicular horizontal directions, the natural frequencies preferably do not exceed 4 cycles per second.
Although the invention has been described with reference to embodiments of clothes washer and spin drying machines for domestic use, the use of the invention is not restricted to the said machines. Notably the invention may advantageously be used also in centrifuges for various industrial uses and, generally, anywhere 'where rapidly rotating eccentrically loaded machine components have to be used.
What is claimed is:
1. A suspension system for a rotatable drum apparatus comprising a frame means, a rotatable drum having a central axis vertically positioned in said frame, a motor for rotating said drum; shaft means interconnecting said motor and said drum, said shaft being aligned with said central vertical axis of said drum and being rotatable with said drum, rigid bushing means for supporting said shaft and damping means for reducing movement of said drum, motor, shaft, and bushing means in horizontal and Vertical directions with respect to said frame, said damping means comprising a resilient rubber element coupled to said motor and said frame, said resilient rubber element having a central axis coincident with the central axis of said shaft and said drum; and a plurality of elastic bands engaging said bushing and said frame, said elastic bands and said resilient rubber element defining an elastic system having an elastic center located on said central axis of said shaft.
References Cited UNITED STATES PATENTS 2,078,445 4/ 1937 Geyer 24818 2,647,591 8/ 1953 Young 248-18 X 2,746,569 5/ 1956 Castner 248-18 X 3,114,705 12/1963 Pribonic et a1. 248-18 X 3,268,082 8/1966 Galin 210-364 FOREIGN PATENTS 1,166,138 6/1958 France. 1,188,513 3/1965 Germany.
JOHN PETO, Primary Examiner.