Coupling for transmission of rotation in a synchronous motor

Abstract: The coupling (20) for transmitting rotation in a synchronous permanent magnetic rotor motor with a central rotor shaft (21), the load (24) being for instance the impeller of a drain pump, comprises a cavity (27) that receives one end of the Rotor shaft (21), a radial cam (22) integral with the rotor shaft (21), and a noise and vibration cushioning member which engages with the cam (22). The elastic cushioning member (25) is housed in said cavity (27) compressed and subjected to a friction force in opposition to the rotation of the rotor shaft (21), limited so that it undergoes a cushioning displacement during motor starting under the impacts of the radial cam (22).

Description: The present invention relates to the constituent parts of a coupling between the load and rotor of a single-phase synchronous motor which transmits rotation to the load, such as the coupling between the rotor and the impeller of a drain pump, in order to eliminate noise and vibrations. PRIOR ART ES-2053372 (N° P9200335) describes a coupling of a drain pump impeller to the rotor shaft of its synchronous motor with a permanent magnetic rotor. The pump impeller has an internal cavity where the rotor shaft is coupled, sealed with a cap. At one end the rotor shaft for coupling to the impeller has an integral coupling cam, fitted with a radial drive catch, which moves back and forth in a free travel inside the impeller chamber for off-load pump starting. The coupling for rotation transmission is realized by means of a radial stopper integral with the impeller, and in its chamber it occupies a circular sector, which has a restricted angle in order to provide the rotor shaft and its drive catch with sufficient angle of free travel for starting the motor by vibration in either of the two directions of rotation. The drive catch engages afterwards with the impeller stopper and makes it turn at synchronous speed. To cushion the impacts of the drive catch against the impeller stopper in both directions of rotation the latter has a cushioning piece inserted made of elastomer material which protrudes laterally from both ends of the stopper in order to absorb the impacts and thereby reduce noise and vibration. This coupling solution has the drawback of being short-lived due to fatigue breakage of the cushioning stopper as a result of the heavy impacts against it, which cannot be remedied by making it thicker because said free angular play should not be reduced. EP-514272 discloses a drain pump impeller coupling solution for transmitting the rotation of its synchronous motor in which a stopper integral with the impeller has cushioning devices formed or attached, consisting of springs in the form of flexible tabs on either side of the stopper. This solution also has a service life problem due to fatigue. EP-474004 discloses a solution for the coupling of the rotor shaft to the rotor of a synchronous motor for transmitting rotation, which has an internal rubber ring attached to the rotor with two integrated stop lugs that impact against a radial cam drive catch attached to the rotor shaft, in a respective direction of rotation of the rotor, and it is an attached part made entirely of rubber affixed to the impeller. This solution also has a service life problem due to fatigue in the rubber cushioning ring attached to the impeller. EP-A-0723329 which represents the closest prior art, discloses a coupling for transmitting rotation to a load from a synchronous motor with a permanent magnetic rotor, wherein the load receives one end of the rotor shaft and the transmission coupling comprises a transmission cavity formed in the interior of an integral box of the rotor placed on the opposite end of the rotor shaft, a radial cam integral with the shaft, a noise and vibration cushioning member that engages with the cam, and a rotation transmission tooth integral with the rotor that engages with the cushioning member, wherein said cavity is covered with a cap, is uniformly cylindrical, and houses the radial cam, the transmission tooth and the cushioning member, and the cushioning member is made of elastic material and is movable into the cavity providing a certain friction against the walls of the cavity in opposition to the rotation of the rotor shaft. DISCLOSURE OF THE INVENTION The object of the present invention is a coupling for the transmission of the rotor rotation to the load in a permanent magnetic rotor synchronous motor, such as a drain pump motor, as defined in claim 1. The transmission coupling according to the invention is realized in a chamber formed either inside the load or in the interior of an integral box (33) of the rotor, and it comprises a solution to prevent vibration and noise during the off.load starting of the motor as well as while the engine is running off load, as for instance when there is hardly any water to discharge in a pump. The coupling has the advantage of its easy construction, since it simplifies the conformation of the impeller or the rotor through doing away with the integral stopper contained in the known solutions. The cushion stopper is made of a single piece, of a regular configuration, which is fitted compressed in the coupling cavity between two surfaces substantially perpendicular to the rotor shaft. In the transmission coupling according to the invention two effects take place for the cushioning of the impacts that occur on the cushioning member: elastic deformation of the cushioning member as a result of the impacts with the cam drive catch, and angular displacement of the cushioning member, which extends the duration of the impact whilst its magnitude is decreased in relation to the known solutions. The displacement of the cushioning member depends on its compression between the two aforesaid engaging surfaces, but the result obtained is not affected substantially by the state of the surfaces nor by the characteristics of the cushioning member material. To achieve such cushioning displacement through its conformation and angular extension, the cushioning member undergoes a friction force in the cavity, which is overcome in the motor starting interval of time by the impacts produced against the cam drive catch, whereas said friction force has to be higher than the force exerted against the coupling cam when the motor is running so that engagement takes place with the drive catch at synchronous speed, while the cushioning member remains stationary, compressed in the axial direction between said two surfaces of the cavity, and the friction force acting on said surfaces to transmit rotation to the load. Besides cushioning the transmission noise and vibration, the transmission coupling according to the invention has a long service life as the cushioning stop member does not undergo any permanent deformation or substantial fatigue. DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a drain pump according to the invention, wherein the coupling is realized in a cavity in the pump impeller. FIG. 2 is a cross-sectional view according to line II-II in fig. 1. FIG. 3 is a cross-sectional view of a drain pump according to the invention, wherein the transmission coupling is realized in a cavity in the motor rotor. DETAILED DESCRIPTION OF THE INVENTION With reference to figures 1 to 2, an initial preferred embodiment of the invention is a coupling 20 for the transmission of the rotation of rotor 15 to impeller 24 of a drain pump, wherein impeller rotor shaft 21 is attached to permanent magnet rotor 15 and to a coupling cam 22, which has a free travel clearance alpha during starting (fig. 2). The transmission coupling comprises a uniformly cylindrical cavity 27 inside the impeller, coupling cam 22 provided with a drive catch 22 a housed in the internal cavity 27 in the impeller (fig. 2), a cushioning member 25 for transmitting rotation, also housed in cavity 27, and a cap 26 for cavity 27 traversed by rotor shaft 21. Coupling cam 22 is attached to end 21 a of the rotor shaft adjacent to the pump body. Cap 26 is disc-shaped. Cushioning member 25 has a cross section in the form of a ring gear sector, the larger arc of which is approximately the same as that of cavity 27, and it is positioned in the radial direction juxtaposed to the cylindrical wall of cavity 27, and in the axial direction fitted between wall 24 a of impeller 24 and the inner surface of cap 26, and compressed by them. Thus, during motor starting, cushioning member 25 permits free turn alpha of the cam and undergoes a displacement with friction against the surface of said walls 24 a and 26, and after starting drive catch 22 a pushes the now stationary cushioning member 25 subjected to a friction force in opposition to the rotation of the rotor shaft 21, and drives impeller 24 to transmit rotation. With reference to figure 3, a second embodiment according to the invention is transmission coupling 30, wherein rotor shaft 31 is driven by the rotor by way of the transmission coupling. Transmission coupling 30 comprises a uniformly cylindrical cavity 37 in a box 33 attached to rotor 16, a coupling cam linked to rotor shaft 31 and housed in cavity 37, a cushioning member 35 and a cap 36 integral with box 33 and traversed by rotor shaft 31. The cushioning member 35 is made as in the coupling embodiment 20 (fig. 1) described previously, and it is engaged in cavity 37 compressed axially between wall 33a of box 33 and the inner wall of cap 36. Box 33 integral with rotor 16 drives cam 32 and rotor shaft 31 in synchronous rotation by way of cushioning member 35. Cam 32 is provided with a radial catch 32a, which is driven by cushioning member 35 for the transmission of rotation to rotor shaft 31, being subjected to said friction force in opposition to the rotation.

Claims: Coupling for transmitting rotation to a load (24,34) from a synchronous motor with a permanent magnetic rotor (15,16), wherein the load (24,34) is driven for rotation by a central rotor shaft (21,31), and the transmission coupling (20,30) comprises a transmission cavity (27,37) inside the load or in the interior of an integral box (33) of the rotor, which receives one of the ends of the rotor shaft (21,31), a radial cam (22,32) integral with the rotor shaft (21,31), and a noise and vibration cushioning member (25,35) housed in said cavity (27,37) that engages with the cam (22,32), characterised in that said cavity (27,37) is covered with a cap (26,36), is uniformly cylindrical, and houses the radial cam (22,32) and the cushioning member (25,35), and the cushioning member (25,35) is made of elastic material and is housed in the cavity (27,37) compressed in axial direction, between the cap (26,36) and a surface (24a,34a) of the cavity (27,37) and subjected to a friction force in opposition to the rotation of the rotor shaft, acting on the said surfaces to transmit rotation to the load (24,34). The transmission coupling of claim 1, wherein the cushioning member (25,35) is subjected to impacts in boths directions against the radial cam (22,32) during motor starting and undergoes a cushioning displacement against said friction force. The transmission coupling (20) of claim 1, wherein said transmission cavity (27) is the interior of a drain pump impeller (24), the rotor shaft (21) is integral with the rotor (15) and the radial cam (22) transmits rotation to the impeller (24) via the cushioning member (25). The transmission coupling (20) of claim 1, wherein said transmission cavity (37) is conformed in the interior of a integral box (33) of the rotor, the rotor shaft (31) is integral with the motor load (34) and the cushioning member (35) transmits rotation to the rotor shaft (31) via the radial cam (32).

Inventors: ERRASTI URIARTE JAVIER, ERRASTI URIARTE, JAVIER
Applicants: FAGOR S COOP, FAGOR, S.COOP
Application year: 1999
Main classification: F04D13
IPC codes: F04D13, F16D7