Device for transmitting power from a motor to a compressor

DΞSCRIPglO-

Technical field

The present invention relates to a device for transmitting power from a motor to a compressor which is enclosed in a vessel outside of which the motor is situated. The device includes a rod extending ^" between the motor and compressor and through the wall of the vessel, said rod describing a circulatory movement on either side of said vessel wall when the motor rotates. Background art

A variety of different modes for transmitting power from a motor to a compressor are already known. If the compressor is a refrigerator compressor it is suitable, for different reasons, to use an electric DC motor with brushes, situated inside the compressor vessel and connected via a.rotating shaft to the crank¬ shaft of the compressor. A considerable disadvantage with such a motor is however that it is sensitive to the oil and freon atmosphere prevailing inside the compressor vessel, which lessens its operational reliability.

To avoid this disadvantage it has been proposed to place the motor outside the compressor vessel and to transmit power between the motor and compressor by means of a magnetic coupling having two permanent magnets, of which one is mounted on the compressor shaft and the other on the motor shaft. The compressor vessel wall separates both permanent magnets.

It has been found, however, that this construction is burdened v/ith several disadvantages. Considerable disadvantages are that large torsional oscillations occur between the permanent magnets and that eddy current losses in the vessel wall between the magnets lessen the efficiency. The permanent magnets are furthermore expensive. The Swedish published patent application 362 702 teaches placing an electric motor outside a compressor vessel and connecting one end of the motor shaft to a shaft thrust into the vessel, said shaft forming an angle with the irst-mentioned

shaft and which, on rotation drive s the compressor with reciprocatory strokes . The rotating movement of the shaft thrust into the vessel is taken up by a non-rotating, but circulating collar surrounding the sha , and connected to a flexible diaphragm forming a gas-tight wall betv/een motor and vessel.

It is also known from the US patent 1 378 118 to place a motor outside a compressor vessel. For transmission of the motor power to the compressor a circulatory rod is used, provided at the middle with an annular convex surface gliding on an annular concave surface in a bearing fixed in the appa¬ ratus casing during the circulatory movement of the rod. The necessary seal between motor casing and compressor vessel is provided by an elastic bellow attached between a portion of the rod and a wall between the motor casing and compressor vessel. The device illustrated in the Italian patent 58 166 is similar to the one shown in the above-mentioned _Lmerican patent, but dif ers therefrom primarily in that the seal between the compressor vessel and the electric motor is provided with the aid of a resilient packing, surrounding a portion of the circu¬ latory shaft and engaging against walls in the compressor vessel, and in that a substantial portion of said shaft is sur¬ rounded by the electric motor.

Even though the apparatus described in the three publica- tions above functions more or less satisfactorily they are burdened with certain drawbacks. One drawback is that the mount¬ ing of the angularly positioned rotating shaft in the Swedish published specification 362 702 and of the circulatory rods in both the other patent specifications become complicated and expensive, and that the sealing between the compressor vessel and electric motor will be imperfect and/or deteriorate rapidly. Another drawback is that the unit comprising motor and compressor obtains large dimensions along the motor shaft and/or at right angles thereto, which makes the unit unsuitable for use in smaller refrigerators intended for installing in small boats and caravans, for example.

0_.FI

Disclosure of the invention

One object of the present invention is to provide a device of the kind mentioned in the introduction, with which the drawbacks of previously known devices have been circum- vented.

This object is achieved by the device in accordance with the invention being given the characterizing features disclosed in the patent claims. Brief description of drawings Figure 1 is a sectional side view of a motor-compressor unit including the device in accordance with the invention.

Figure 2 is a sectional view of a portion of the device in Figure 1 and

Figure 3 is a sectional view of a second embodiment of a portion of the device in Figure 1. Preferred embodiments

In Figure 1 there is illustrated an electric motor 1, the stator 1a of which is fixed in a housing 2 including a cylindrical casing 2a. The rotor 1b of the motor 1 comprises the conventional electrical components and is formed as a hollow cylinder 3» in which an enlarged portion 4a of a shaft 4 is attached. A second enlarged portion b of the shaft 4 coacts with conventional brushes 5. The rotor 1b is rotatably mounted in the housing 2 by means of ball bearings 6 and 7. A vessel 8 enclosing a compressor 10 and consisting of a bowl-shaped casing 8a with a base portion 8b is attached by bolts 9 to the housing 2 of the motor 1. On the base portion 8b there is attached a hollow cylinder 11 having ball bearings 12 in which a hollow cylinder 13 is rotatably mounted. At one end of the cylinder 13 there is attached a cylindrical end wall 14 eccentrically connected to a crank shaft 15, on which there is rotatably mounted the crank 16 of the piston compressor 10 which is attached to the cylinder 11.

A rod 17 is used for transmission of the power from the motor 1 to the compressor 10, the left-hand end of this rod, illustrated in Figure 1 , is eccentrically mounted in a cavity in the portion 4a via a ball bearing 18, the right-hand end of

- UREAU ^* _0MPI W1PO -

the rod being eccentrically mounted via a hall bearing 19 in a cavity formed in the end wall 14.

The middle portion of the rod 17 is sealingly and resiliently attached to a flexible diaphragm 20 of elastomeric material, such as rubber. The diaphragm 20 forms the necessary . separating wall between the electric motor 1 and the freon- rich atmosphere inside the compressor vessel 8, and. is also a support for the middle portion of the rod. The diaphragm 20 is substantially circular and its outer edges are sealingly fixed between the housing 2 and base portion 8b. As a result of the excess pressure in the vessel 8, the diaphragm is given an annular curvature or bulge 20a, allowing a certain amount of movement of the central portion of the diaphragm along and at angles to the central axis of the motor 1. The end of the rod 17 mounted in the portion 4a describes a circular, circulatory movement in the vertical plane of Figure 1 when the rotor 1b rotates. Since the central axis for the middle portion of the rod 17 is connected to the diaphragm 20 at a point a, situated in the Figure under the central axis of the motor 1, the right-hand end of the rod mounted in the end wall 14 will describe an elliptical movement. Since the right-hand end of the rod 17, due to its eccentric attachment in the end wall 14, can only describe a circular movement in the vertical plane of the figure, the axial movement component thereby occurring must be taken up, which in the present embodiment takes place by the rod being allowed to glide axially in the ball bearing 19. During the circulatory movement of the rod, its middle portion will also be displaced, the diaphragm thus being given a reciprocatory oscillating movement ₀ The magnitude of the oscillatory movement component can be reduced by making the middle portion of the rod 17 substantially parallel to the centre line , and allowing both ends of the rod connected to the middle portion to form a small angle to the middle portion, as illustrated in Figure 1. The reason for the point a being displaced downwards relative to the central axis m is that the right-hand end of the rod 17 thus comes further down in the compressor casing, whereby

________ ^'

the whole compressor portion can be made lower and therefore more central relative the motor 1.

Another method of lowering the right-hand end of the rod 17 relative to the central axis is to allow its middle portion connected to the diaphragm to intersect the central axis m, whereby no reciprocatory diaphragm movement occurs, and to bend the right-hand portion of the rod outwards (down¬ wards) immediately to the right of the diaphragm in the mode illustrated in Figure 3- The result of this measure is to give the right-hand end of the rod 17 an elliptical, circulatory movement which is translated in the ball bearing 19 (also formed as a sliding bearing) to a circular movement component in the vertical plane of the figure and a linear movement component in the longitudinal direction of the rod. The attachment of the diaphragm 20 at the middle portion of the rod 17 is illustrated in detail in Figure 2. In order that the diaphragm a) will firmly support the rod and hold its middle portion at a substantially constant distance from the housing 2 and base portion 8b, b) that it will with- stand the stresses it is subjected to during operation, and c) that it will be able to seal against the middle portion, it must be relatively stiff although flexible and somewhat re¬ silient. The diaphragm 20 consists of rubber, and for the reasons above it must be made thick-walled, resulting in that the inner shear stresses in the material will be large, and accelerate the deterioration of the diaphragm, or it must be constructed in another way. According to a suitable embodiment, the diaphragm 20 has been put together from three equally large rubber layers 20a, 20b and 20c, lying against each other except in the area of the middle of the rod 17, where they are separated by steel washers 21 , put on the middle portion of the rod. Steel washers 22 and 23 engage against both outer surfaces of the layers 20a and 20 c facing away from the washers 21, the edges of the washers 22 and 23 being belled outwards from the respective layer so as not to cause wear of said layer during operation,- The details 20a - c, 21, 22 and 23 are forced together by nuts 24 and 25, which are threaded onto the middle portion

of the rod 17, so that the edges of the holes in the layers surrounding said middle portion are sealingly pressed against the cylindrical surface thereof. As a result of the described arrangement, the shear forces acting on the diaphragm are reduced and a tight stiffening joint between the rod middle portion and the diaphragm 20 is obtained.

Other embodiments of the device described above and illustrated on the drawings are possible without departing the from/inventive concept. The invention is limited solely by the disclosures in the patent claims.

B\ R-ΞA

0.MP1