EP3418568A1 - Piston for the drive unit of a refrigerant compressor - Google Patents

Abstract

Shown is a piston for the drive unit of a refrigerant compressor, the piston comprising a cylindrical base body (1) and a ring (6,9,10) made of plastic, wherein the base body has at least one circumferential groove (3,11), in which the ring is held. In order to keep the leakage losses of refrigerant as low as possible even at low speeds, it is provided that the ring (6,9,10) has a higher coefficient of thermal expansion than the base body (1) and the ring (6,9,10) at room temperature Piston has an outer surface (12,17) which is aligned with the peripheral surface of the cylindrical piston outside the groove (3,11). During operation of the piston, the latter heats up, whereby the ring expands more strongly than the main body due to the higher coefficient of thermal expansion, thereby reducing the mating clearance between the piston and the cylinder in which the piston is inserted.

Description

FIELD OF THE INVENTION

The present invention relates to a piston for the drive unit of a refrigerant compressor, the piston comprising a cylindrical base body and a ring made of plastic, wherein the base body has at least one circumferential groove in which the ring is held.

The drive unit is usually enclosed by a, in particular hermetically sealed, housing so that the refrigerant compressor forms a closed unit relative to the environment.

STATE OF THE ART

Refrigerant compressors (refrigerant compressors) have in one embodiment in a hermetically sealed housing on a piston-cylinder unit and provided for the drive of the piston-cylinder unit electric motor. The piston is usually designed as a linear piston.

In order to increase the efficiency of the refrigerant compressor, the mating clearance between piston and cylinder should on the one hand be as large as possible in order to reduce the friction, but on the other hand be as small as possible, so that the leakage losses of the refrigerant are low. A deviating from the cylindrical shape for these purposes, the shape of the piston can be made by grinding only with considerable additional effort. Thus, a piston whose peripheral surface is not a cylinder jacket falls away for practical reasons for adjusting the mating clearance.

Slotted, arranged in piston grooves and biased piston rings are in the art of internal combustion engines state of the art. However, these piston rings are only useful in a large mating clearance between the piston and cylinder, otherwise the leakage losses through the Nutspalten be higher.

For other types of refrigerant compressors, it is known to provide for better sealing between the piston and cylinder grooves in the peripheral surface of the cylinder, wherein in each groove a plastic ring, for example made of polytetrafluoroethylene, is arranged, see the swash plate type compressor in the US Pat. No. 4,697,992 A , In any case, the outer diameter of the plastic ring is greater than the diameter of the piston and it flows through the distance between the plastic ring and piston in any case refrigerant, which is disadvantageous.

Refrigerant compressors with variable-speed drive, so-called VSD (variable speed drive) compressors, in particular with linear drive, are often operated at low speeds. Leakage losses are nearly independent of speed, making their percentage of total losses at low speeds higher than at high speeds.

OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a piston for a drive unit of a refrigerant compressor, which avoids the disadvantages mentioned above. In particular, the leakage losses of refrigerant should be kept as low as possible, even at low speeds.

PRESENTATION OF THE INVENTION

For this purpose, in a piston for the drive unit of a refrigerant compressor, the piston comprising a cylindrical base body and a ring made of plastic, wherein the base body has at least one circumferential groove in which the ring is held, provided that the ring has a higher coefficient of thermal expansion than the main body and the ring at room temperature of the piston has an outer surface which is flush with the peripheral surface of the cylindrical piston outside the groove.

In simple terms, the ring does not project beyond the piston in the radial direction at room temperature of the piston. In longitudinal section through the piston, the peripheral surface of the piston with ring is consequently a straight line. In the case of an uncoated piston, the base body alone forms the piston and the ring does not protrude in the radial direction beyond the groove of the base body.

The cylindrical base body of the cylindrical piston thus has a recess which is filled with plastic. During operation of the piston, the latter heats up, whereby the ring expands more strongly than the main body due to the higher coefficient of thermal expansion. The main body will usually be metallic or ceramic. In a ceramic base body, the leakage losses are low in a small mating game, which is important at low speeds. In a large mating game, the friction losses are low, which is important at high speeds. A ceramic base body has the advantage that it has a smaller thermal expansion coefficient than the metallic cast housing and therefore the mating clearance becomes greater with increasing operating temperature. At low speeds, the operating temperature is smaller and thus the mating game smaller and subsequently the leakage losses are low.

At high speeds, it is the other way round, the mating game is larger here and thus the friction losses are low.

The ring expands mainly in the radial direction, thereby reducing the mating clearance between the piston and the cylinder in which the piston is inserted. As a result, the leakage losses are reduced, but the friction between piston and cylinder is only minimally increased, if at all. The sum of the losses from leakage and friction is thus reduced compared to conventional pistons without ring, the efficiency of a refrigerant compressor, which is equipped with the piston according to the invention, increases.

In other words, it can thus be provided that at the operating temperature of the piston, which is above 50 ° C, in particular between 60 and 120 ° C, the outer diameter of the ring is greater than the outer diameter of the remaining cylindrical piston.

A particularly good attachment of the ring on the body can be achieved when the ring fills the entire cross section of the groove.

In a possible embodiment of the piston according to the invention it is provided that the ring is made by coating the base body with plastic and in particular fills the entire cross section of the groove. It must therefore not laboriously a possibly slotted ring are raised over the body, but the ring is made directly in the groove of the body, the groove is used as a kind of shape for the ring. Plastic, which extends beyond the coating in the radial direction over the desired cylinder diameter, can then be removed, for example by grinding. The ring thus has an outer surface in the form of a cylinder jacket, while the inner surface has the shape of the groove.

The complete filling of the groove through the ring creates a closed profile of the ring. In the US Pat. No. 4,697,992 A however, the profile of the ring is rather U-shaped and thus open.

The ring could also be made by molding the metallic base body with plastic. But it is also conceivable that a finished ring of plastic is pressed onto the body and / or glued.

A first variant of the invention provides that exactly one groove is provided only in the circumferential surface of the base body. Consequently, the piston then has only one ring in the circumferential surface of the main body. The ring or the groove are usually closer, in particular as close as possible, in the end face of the piston than at the other axial end. The end face is that most flat surface, which is directed in the operating condition of the piston in the interior of the cylinder, where the compression takes place. However, the end face may have small elevations in the axial direction, which protrude into free spaces of the valve plate. Furthermore, the end face can also have an open position for a valve in order to be able to reduce the clearance between the piston and the valve plate. Both are measures to minimize the dead space.

The first variant usually requires that at room temperature of the piston, the outer diameter of the ring is equal to the outer diameter of the body outside the groove and at the operating temperature of the piston, the outer diameter of the ring is greater than the outer diameter of the body outside the groove.

A second variant of the invention provides that at least two grooves are provided only in the peripheral surface of the piston are and in each groove a ring is arranged. With two rings, the seal can be further improved.

It can be provided that the entire end face and at least a portion of the adjoining the end face peripheral surface of the body, in particular the entire peripheral surface, are provided with a continuous plastic layer which connects the two rings together so that the rings are part of the plastic layer, said the radial thickness of the plastic layer on the peripheral surface of the base body is smaller than the radial thickness of the rings. The plastic layer reduces the heat transfer from the piston to the sucked gas.

The plastic layer on the end face may have a different, in particular a greater, thickness than the plastic layer on the peripheral surface. In any case, increases at room temperature, the outer diameter of the ring of the first variant by the thickness of the plastic layer. Because rings and plastic layer are produced in a coating process, which of course must also result in plastic layer with a cylindrical peripheral surface of the piston. At the operating temperature of the piston plastic layer and rings will expand in the radial direction, the rings expand more than the rest of the plastic layer on the peripheral surface of the body due to their greater thickness. It will therefore seen from the outside of the plastic where the rings are, bulge, so that there are two annular, surrounding the piston increases. In the operating condition of the piston, these elevations will engage the cylinder and seal the cylinder volume accordingly.

The cross section of the groove can be smaller than a semicircle in the first and second variants, for example a semicircle or a circular segment. Generally are different Groove shapes possible, so also grooves with eg rectangular cross section.

A third variant of the invention provides at least one groove, which reduces both the end face of the cylindrical base body and the adjoining peripheral surface of the base body. In other words, a groove or a ring is produced at the edge between the front and peripheral surface of the base body.

It can be provided that the ring at room temperature of the piston has a first outer surface which is aligned with the peripheral surface of the cylindrical piston outside the groove, and has a flat second outer surface which is aligned with the end face of the cylindrical piston outside the groove. In other words, the ring does not protrude beyond the imaginary cylindrical surface of the main body before making the groove. With this shape of the ring, the sealing effect of the ring at higher pressures, which also cause a higher leakage, be further increased: in the operating state acts on the piston, more precisely on the end face, in the axial direction, a variable gas pressure, the elastic material of the ring outward, radially beyond the body out, displaced.

This may be assisted by the shape of the groove, for example by a first surface of the groove being parallel to the axis of the cylindrical base body and a second surface of the groove enclosing an obtuse angle with the first surface of the groove. It would also be possible that a first surface of the groove extends parallel to the axis of the cylindrical base body and a second surface of the groove encloses a right angle with the first surface of the groove.

It is conceivable that a groove or a ring is combined at the edge between the front and peripheral surface of the body one or more further grooves or rings only in the peripheral surface of the body. In other words, a groove is provided which reduces both the end face of the cylindrical base body and the adjoining peripheral surface of the base body, and additionally at least one groove only in the peripheral surface of the base body.

The rings and / or the plastic layer can be made of polyaryletherketones (PAEK), in particular of polyetheretherketones (PEEK), or at least contain them. Polyaryletherketones (PAEK) are high-temperature resistant thermoplastics. The good strength of the semi-crystalline aromatic polymers is retained even at higher temperatures. In addition, PAEK materials show very good impact strength at low temperatures, high mechanical resistance to change, very low creep and good sliding and wear behavior. Accordingly, other plastics with good sliding and wear behavior for the rings or coatings of the invention are suitable.

The invention also includes a piston in a drive unit for a refrigerant compressor, thus a drive unit for a refrigerant compressor with piston, wherein the piston is designed according to the invention and the ring of the piston is dimensioned so that at the operating temperature of the piston by the expansion of the ring a seal the cylinder cross-section of the cylinder of the drive unit results.

In this case, the piston is generally designed as a linear piston, so it moves exactly along a straight line, wherein the rotational movement of the electric motor of the drive unit is converted into a linear motion with a connecting rod.

The invention also relates to a refrigerant compressor comprising, in particular hermetically dense, housing and disposed therein a drive unit with piston according to the invention. The refrigerant compressor may be used, for example, for cooling the interior of a refrigerator or freezer.

The refrigerant compressor may be configured as a variable speed compressor, as a so-called variable speed compressor. Because with these speed-controlled compressors, the percentage share of leakage losses in the total losses at low speeds is higher than at high speeds, so that the piston according to the invention causes a large relative reduction of leakage losses. Of course, the invention is also applicable to fixed-speed refrigerant compressors.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be explained in more detail with reference to exemplary embodiments. The drawings are exemplary and are intended to illustrate the inventive idea, but in no way restrict it or even reproduce it.

Fig. 1

einen Schnitt durch einen erfindungsgemäßen Kolben, erste Variante, mit einer Nut in der Umfangsfläche, ohne Nutbeschichtung,

Fig. 2

den Kolben aus Fig. 1 mit Nutbeschichtung,

Fig. 3

den Kolben aus Fig. 2 mit bearbeiteter Nutbeschichtung,

Fig. 4

den Kolben aus Fig. 3 bei Betriebstemperatur, im Zylinder angeordnet,

Fig. 5

einen Schnitt durch einen erfindungsgemäßen Kolben, zweite Variante, mit zwei Nuten in der Umfangsfläche, mit bearbeiteter Nutbeschichtung,

Fig. 6

den Kolben aus Fig. 5 bei Betriebstemperatur, im Zylinder angeordnet,

Fig. 7

einen Schnitt durch einen erfindungsgemäßen Kolben, dritte Variante, mit einer Nut in der Stirnfläche, mit Nutbeschichtung,

Fig. 8

den Kolben aus Fig. 7 bei Betriebstemperatur, im Zylinder angeordnet.

Showing:

Fig. 1

a section through a piston according to the invention, first variant, with a groove in the peripheral surface, without groove coating,

Fig. 2

the piston off Fig. 1 with groove coating,

Fig. 3

the piston off Fig. 2 with machined groove coating,

Fig. 4

the piston off Fig. 3 at operating temperature, arranged in the cylinder,

Fig. 5

a section through a piston according to the invention, second variant, with two grooves in the peripheral surface, with machined groove coating,

Fig. 6

the piston off Fig. 5 at operating temperature, arranged in the cylinder,

Fig. 7

a section through a piston according to the invention, third variant, with a groove in the end face, with groove coating,

Fig. 8

the piston off Fig. 7 at operating temperature, arranged in the cylinder.

WAYS FOR CARRYING OUT THE INVENTION

The pistons according to the invention are suitable for refrigerant compressors comprising a drive unit with a piston-cylinder unit for the cyclical compression of a refrigerant and an electric motor for driving the piston-cylinder unit. The piston-cylinder unit comprises a piston which is guided linearly displaceable in the cylinder 2 of a cylinder housing, and as an integral part comprises a cylindrical base body 1. In the cylinder housing and the motor shaft of the rotor of the electric motor is rotatably mounted. The stator of the electric motor carries the cylinder housing and is mounted via spring elements in the interior of the hermetically sealed housing of the refrigerant compressor.

Fig. 1 shows a piston of the first variant, with only one groove 3 in the peripheral surface 4. The groove 3 is not filled or coated with plastic, it has an approximately semicircular cross-section. The main body 1 has a bore in the direction of the axis 16, in which bore a connecting rod can be introduced, the connecting rod eye is held by a bolt which is inserted into the transverse bore of the base body 1 in the base body 1. To the peripheral surface 4, which has the shape of a cylinder jacket, includes the end face 5, which has the shape of a circular disk. The end face 5 is directed in the operating state of the piston in the interior of the cylinder volume, where the compression takes place.

In Fig. 2 the piston is out again Fig. 1 shown, wherein the groove 3 is now already coated with plastic, thus a ring 6 is in the groove 3. The outer surface of the ring 6 projects radially beyond the peripheral surface 4. The plastic has also deposited in the axial direction outside the groove 3 on the peripheral surface 4. Therefore, the peripheral surface 4 must be processed so that the supernatant of the ring 6 can be removed.

Fig. 3 shows the piston Fig. 2 with machined groove coating. The ring 6 now has a cylindrical jacket-shaped outer surface 17, which has the same diameter as the peripheral surface 4 of the main body outside the groove 3. The piston thus has, when it is not in operation, a completely flat peripheral surface.

Fig. 4 shows the piston Fig. 3 at operating temperature, so if this is heated by the movement in the cylinder 2. In this case, the ring 6 expands in the radial direction, so that it protrudes beyond the peripheral surface 4 of the main body 1 and thereby the distance between the peripheral surface 4 and cylinder 2, the mating game 7, closes. The first in the sectional view of the outer surface of the ring 6 is slightly curved here, thereby forming a convex seal. This sealing ring is continuous at both axial ends, ie without kinking or spacing, in the peripheral surface 4 via.

Fig. 5 shows a second variant of a piston according to the invention, with two grooves 3 in the peripheral surface 4 of the base body 1. Here, unlike in Fig. 2 , Not only the grooves 3 coated with plastic or poured, but it is the main body 1 at the end face 5 and on the peripheral surface 4 completely surrounded by a plastic layer 8. This results in two rings 9, compared to Fig. 3 around the plastic layer 8 are thicker. This results in a resulting circumferential surface of the piston, which has exactly the shape of a cylinder jacket, the plastic layer 8 must be processed accordingly. In Fig. 5 this processing has already taken place. In Fig. 5 can also be seen that the plastic layer 8 over the end face 5 has a greater thickness than on the peripheral surface 4. Thus, a particularly good thermal insulation of the base body 1 can be achieved on the end face 5.

Fig. 6 shows the piston Fig. 5 at operating temperature, when this is arranged in the cylinder 2 and is moved. As a result of the heating of the basic body 1, the rings 9, which are formed integrally with the plastic layer 8, are also heated. Since the rings 9 have a greater thickness than the plastic layer 8 next to the grooves 3, the rings 9 experience a greater thermal expansion and each form an annular bulge, which projects beyond the remaining plastic layer 8, which is arranged on the peripheral surface 4, radially. Since the rings 9 and the plastic layer 8 form a part, has the contour of the outer peripheral surface of the piston - in the longitudinal section of the Fig. 6 seen - a steady course. Therefore, this course causes less friction than a ring which would be inserted into the groove 3 and necessarily firstly in the groove would have to play in the axial direction of the piston and secondly could hardly connect steadily to the adjoining the groove 3 peripheral surface of the piston ,

Fig. 7 shows a section through a third variant of a piston according to the invention with a groove 11 in the end face 5. Again, the groove 11 is first filled with plastic, for example coated or overmoulded with plastic or a finished ring pressed and / or glued, and then the If necessary, external surfaces of the piston machined again to remove any protrusion of the ring 10 beyond the groove 11 addition. In Fig. 7 the piston is shown in the finished state at room temperature.

The groove 11 is made so that both the end face 5 of the cylindrical base body 1 and the adjoining peripheral surface 4 of the main body 1 are reduced where the two surfaces collide. The ring 10 has at room temperature of the piston on a first outer surface 12 which is aligned with the peripheral surface of the cylindrical piston, here the peripheral surface 4, outside the groove 11, and a second, flat outer surface 13, with the end face 5 of the cylindrical piston outside the groove 11 is aligned. The ring 10 thus restores the original cylindrical shape of the main body 1.

The first flat surface 14 of the groove 11 extends in this example parallel to the axis 16 of the cylindrical base body 1 and the second flat surface 15 of the groove 11 includes an obtuse angle with the first surface 14 of the groove 11 a. The obtuse angle is between 100 ° and 120 °, here at about 110 °. It would also be conceivable, however, to have a right angle between the first planar surface 14, which runs parallel to the axis 16, and the second planar surface 15.

Fig. 8 shows the piston Fig. 7 at operating temperature, when the piston is arranged in the cylinder 2 and is moved. By prevailing in the cylinder 2 gas pressure, represented by parallel arrows in the direction of the end face 5, the material of the ring 10 is compressed in the axial direction and due to the material stresses arising in the interior, the ring 10 expands to the outside. The greater the pressure on the end face 5 or the ring 10, the greater the sealing effect of the ring 10. This is advantageous because the higher the pressure in the cylinder 2, the higher the leaks are.

LIST OF REFERENCE NUMBERS

1

Basic body of the piston

2

cylinder

3

groove

4

Peripheral surface of the main body 1

5

End face of the main body 1

6

ring

7

mating game

8th

Plastic layer

9

ring

10

ring

11

groove

12

first outer surface of the ring 10th

13

second outer surface of the ring 10th

14

first surface of the groove 11th

15

second surface of the groove 11th

16

Axle of the main body 1

17

outer surface

Claims (15)

Piston for the drive unit of a refrigerant compressor, the piston comprising a cylindrical base body (1) and a ring (6,9,10) made of plastic, wherein the base body has at least one circumferential groove (3,11), in which the ring is held, characterized in that the ring (6,9,10) has a higher coefficient of thermal expansion than the base body (1) and the ring (6,9,10) at room temperature of the piston has an outer surface (12,17) with the peripheral surface of the cylindrical piston outside the groove (3,11) is aligned. Piston according to claim 1, characterized in that at the operating temperature of the piston, which is above 50 ° C, in particular between 60 and 120 ° C, the outer diameter of the ring (6,9,10) is greater than the outer diameter of the remaining cylindrical piston , Piston according to claim 1 or 2, characterized in that the ring (6,9,10) fills the entire cross-section of the groove (3,11). Piston according to one of the preceding claims, characterized in that the ring (6,9,10) by coating the base body (1) is made with plastic. Piston according to one of the preceding claims, characterized in that exactly one groove (3) is provided only in the circumferential surface (4) of the main body (1). Piston according to claim 5, characterized in that at room temperature of the piston, the outer diameter of the ring (6) is equal to the outer diameter of the base body (1) outside the groove (3) and at the operating temperature of the piston, the outer diameter of the ring (6) is greater than the outer diameter of the base body (1) outside the groove (3). Piston according to one of claims 1 to 4, characterized in that at least two grooves (3) are provided only in the peripheral surface of the piston and in each groove, a ring (9) is arranged. Piston according to Claim 7, characterized in that the entire end face (5) and at least part of the peripheral surface (4) of the base body (1) adjoining the end face are provided with a coherent plastic layer (8) which surrounds the two rings (9). connects together so that the rings are part of the plastic layer, wherein the radial thickness of the plastic layer (8) on the peripheral surface (4) of the base body (1) is smaller than the radial thickness of the rings (9). Piston according to one of claims 1 to 4, characterized in that at least one groove (11) is provided, which reduces both the end face (5) of the cylindrical base body (1) and the adjoining peripheral surface (4) of the base body (1) , Piston according to claim 9, characterized in that the ring (10) at room temperature of the piston has a first outer surface (12) which is flush with the peripheral surface of the cylindrical piston outside the groove (11) and has a flat second outer surface (13) , which is aligned with the end face (5) of the cylindrical piston outside the groove (11). Piston according to claim 9 or 10, characterized in that a first surface (14) of the groove (11) parallel to Axis (16) of the cylindrical base body (1) and a second surface (15) of the groove (11) forms an obtuse angle with the first surface (14) of the groove. Piston according to one of claims 9 to 11 on the one hand and one of claims 5 to 8 on the other hand, characterized in that a groove (11) is provided, both the end face (5) of the cylindrical base body (1) and the adjoining peripheral surface ( 4) of the base body (1) reduced, and that in addition at least one groove (3) only in the peripheral surface (4) of the base body (1) is provided. Piston according to one of the preceding claims, characterized in that the ring (6,9,10) polyaryletherketones, in particular polyetheretherketones, contains or is manufactured from these. Drive unit for a refrigerant compressor with piston, wherein the piston is designed according to one of the preceding claims, in particular designed as a linear piston, and the ring (6,9,10) of the piston is dimensioned such that at the operating temperature of the piston by the extension of Rings a seal of the cylinder cross-section of the cylinder (2) of the drive unit results. Refrigeration compressor, in particular a compressor with variable speed, comprising a, in particular hermetically sealed, housing and a drive unit arranged therein according to claim 14.

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