EP2954208B1 - Asymmetric reciprocating piston compressor - Google Patents

Description

The invention relates to a reciprocating compressor, in particular a reciprocating compressor for a portable small compressor unit, with a piston driven by a slider-crank drive and a piston movable back and forth in a cylinder and sealed against the cylinder wall, the slider-crank drive being a crank wheel with an eccentric crank pin arranged on a crankshaft as well as a connecting rod arranged between the piston and the crank pin, the piston or piston crown being arranged fixed to the connecting rod axis.

Such reciprocating compressors are usually driven by small, high-speed electric motors, which mesh with a corresponding external toothing of the crank wheel via a pinion on their output shaft.

Small compressor units are often required for so-called "breakdown kits", i.e. for breakdown assistance systems, in particular for the temporary sealing and re-inflation of vehicle tires after air loss. Often other functions are available or can be used by switching, such as using the compressor alone when inflating air mattresses or rubber boats. Both in the manufacture and in the assembly of such small, but high-speed compressors, there should be as little effort as possible and thus cost-intensive manufacturing methods and materials should be avoided, which often leads to the use of simple and lightweight plastics for all kinds of components, including the piston.

In these air compressors, a rotationally symmetrical piston is usually used in a rotationally symmetrical cylinder. Alternatively, pistons and cylinders also have a different cross section together. According to the U.S. 4,765,292 this can also be oval or elliptical, for example.

To reduce costs, these systems do not have a piston joint and the piston is rigidly connected to a crankshaft via a connecting rod. With a right-angled connection between the piston and the connecting rod, the highest sealing ability between the piston and the cylinder is achieved in the dead centers, i.e. in the ends of the movement range of the piston (top dead center = TDC / bottom dead center = BDC). In the middle of the range of motion, the sealing ability decreases, because a deviation of the symmetry axis of the piston from the symmetry axis of the cylinder develops the so-called piston inclination and the piston seal no longer fits perfectly against the cylinder wall.

While the piston inclination during the idle stroke only becomes problematic when the piston compressor is working with a pre-pressure, it is very disadvantageous during the compression stroke, since the maximum sealing capability should be achieved here for the most efficient possible operation of the compressor.

The use of a particularly flexible piston seal does not solve the problem adequately, since such a highly flexible seal reduces the decrease in sealing ability somewhat, but does not prevent the fundamental reduction in sealing ability in the middle range of movement of the compression stroke and thus does not postpone the point in time of maximum or minimum sealing ability . Even at low temperatures, such a piston seal is no longer suitable for preventing the sealability from falling, since the piston seal then hardens.

In the FR 2 752 269 A1 the problem of the reduced sealing ability in the middle range of motion of a piston compressor is prevented by the fact that the axis of the crankshaft of the counterweight designed as a counterweight is offset from the axis of the cylinder so that in the middle range of motion of the compression stroke there is no deviation of the axis of symmetry of the piston from the Axis of symmetry of the cylinder is present and then a maximum sealability is given at this point in time. However, this solution accepts a reduced sealing ability between piston and cylinder in the dead centers, since the piston inclination is then pronounced. The one in the FR 2 752 269 A1 The device described can also be used as a vacuum pump if the direction of rotation of the counterweight is changed.

In order to also remedy the problem of reducing the sealing capability of a reciprocating compressor with a rigid connection between piston and connecting rod in the middle range of motion of the compression stroke, US Pat DE 20 2011 052 002 U1 An air compressor in the form of a reciprocating compressor, in which the piston and thus the upper piston crown is inclined to the connecting rod axis and, when viewed at the dead points, is also inclined to the cylinder axis, and at top dead center (TDC) interacts with a complementary inclined head surface of the cylinder. With a suitable design, this means that during the compression stroke the piston moves with the piston head essentially perpendicular to the cylinder wall and is thus effectively compressed, while during the idle stroke the piston is displaced with an increased inclination towards the cylinder wall and thus ambient air very easily past the piston seal the compression space can flow.

Disadvantages here are the costly manufacture of pistons with connecting rods and cylinders and the necessary inclination-correct assembly of the piston. For example, the cylinder base or the inside of the cylinder head must also be designed to be inclined so that sufficient compression takes place and so that the inclined piston does not hit the cylinder head and be damaged at TDC.

Based on this, the object of the invention was to provide a reciprocating compressor, in particular for a high-speed small compressor within portable / transportable devices, which despite simple manufacture without a piston joint and despite the use of inexpensive materials, a high compression ratio and a high delivery volume even with a kinematic during the lifting movement existing piston inclination and avoids leaks during the stroke movement.

This problem is solved by the features of the main claim. Further advantageous designs are disclosed in the subclaims.

The piston and / or the cylinder are designed in such a way that the sickle-shaped gaps between the piston edge and the cylinder wall that arise during the respective stroke movement due to the relative inclination between the piston axis and the cylinder axis can be sealed.

If a piston in a cylinder can be moved around several axes, the piston shape is aligned with the cylinder due to the relationship between the shape of the piston and the shape of the cylinder. This is the case in TDC and also in BDC when the piston axis and cylinder axis essentially coincide. If this alignment with maximum sealing capability cannot be maintained over the entire range of movement of the piston, a periodic piston movement also leads to a periodic change in the sealing capability between piston and cylinder. During the movement of the piston through the central movement area, the inclination of the piston creates sickle-shaped gaps between the piston wall and the cylinder wall.

The invention solves this problem in that the piston, also understood here as an entire assembly with piston seal, and / or the cylinder seal the sickle-shaped gaps through their geometrical or material-technical design or through accessories. The inventive training made it possible to achieve an increase in performance of up to 20% compared to devices from the prior art.

The piston or piston head is arranged perpendicular to the connecting rod axis.

The piston has an oval-elliptical shape deviating from the circular shape, by means of which the sickle-shaped gaps can be at least partially compensated, the piston being designed so, for example, elastically flexible, compressible or geometrically flexible, that during the entire stroke movement and in the dead centers an elastic seal takes place between the piston and the cylinder wall, of course, in particular with the aid of the elastic or compressible annular piston seal. A simple static-geometric change in the shape or contour of the piston achieves not only an improved seal during the compression stroke also in the middle range of motion, thus a higher compression ratio and also a larger delivery volume, but also a secure seal during the entire idle stroke.

Compared to the known solutions from the prior art, here, for example, compared to the piston head, which is fixed and inclined to the connecting rod axis in the DE 20 2011 052 002 U1 The solution according to the invention thus also offers the advantage that the reciprocating compressor can also be connected downstream of a precompressor due to the secure sealing of the reciprocating piston compressor, which is also present during the idle stroke, that is to say that already precompressed charge air can be applied. This increases the compression ratio again significantly.

The piston according to the invention is of course designed with its oval-elliptical shape deviating from the circular shape in such a way that the large semi-axis is arranged perpendicular or essentially perpendicular to the shaft of the crank wheel.

An advantageous embodiment is that the piston has an oval-elliptical shape, in which the length of the small semiaxis is at least 80% of the length of the major semiaxis. This is a design confirmed by tests, in which, on the one hand, there is sufficient sealing force during the lifting movement and, on the other hand, the friction in the dead centers does not assume any harmful values.

mm und deren große Halbachse eine Länge von $\left(\frac{\mathrm{32,1}}{2}\right)$

mm aufweisen. Überraschenderweise verbessern sich bereits durch eine so geringe Elliptizität des Kolbens mit einem Halbachsenunterschied von nur 0,2 mm das Kompressionsverhältnis und das Fördervolumen erheblich.In such a design according to the invention of small compressors such. B. for a portable breakdown assistance system, such a training is advantageous in that the piston has an oval-elliptical shape, whose small semi-axis $\left(\frac{31.7}{2}\right)$

mm and whose major semi-axis has a length of $\left(\frac{32.1}{2}\right)$

mm. Surprisingly, even such a small ellipticity of the piston with a semi-axis difference of only 0.2 mm significantly improves the compression ratio and the delivery volume.

The piston has a circular shape and the annular piston seal has a varying thickness, in which the maximum thickness is arranged and designed so that the sickle-shaped gaps can be compensated, wherein the piston seal is designed so that an elastic There is a seal between the piston and the cylinder wall. This means that the piston itself does not need to be changed, which allows the use of normal standard pistons, but only the thickness of the annular piston seal in order to achieve simple static-geometric changes in the effectively sealed surface of the piston, the compression ratio and Funding volume improved.

Another advantageous embodiment is that the cylinder has an oval-elliptical shape deviating from the circular shape in its central compression area, through which the sickle-shaped gaps can be at least partially compensated, the annular piston seal being designed so that during the entire stroke movement and in an elastic seal between the piston and the cylinder wall takes place at the dead centers. The additional machining effort required for this on the cylinder is justifiable, especially in the case of cast cylinders, if the pistons, which are usually made of plastic, can be used as cheap standard parts and the cylinder can be reused if necessary.

A further advantageous embodiment consists in that the compensation of the sickle-shaped gap on the piston and / or on the seal is effected by adjusting elements on the piston, in particular by resilient elements or by elements that are acted upon by a pressure medium. In contrast to the use of a highly flexible piston seal, the adaptation takes place dynamically and in a directional manner, depending on the design of the sickle-shaped gap between the cylinder and piston contour, by means of design measures or additional design elements. This procedure enables, among other things, the achievement of the maximum sealing ability at more than just one point in time of the periodic piston movement.

A further advantageous embodiment consists in that the resilient elements are arranged in the piston body, in particular by means of resilient circumferential webs which are formed over a partial circumference of the piston by kidney-shaped recesses that are concave towards the center of the piston

A further advantageous embodiment consists in that the compensation of the sickle-shaped gap on the piston and / or on the seal takes place by means of inserted shaped elements (intermediate elements). The advantage here is that only in the Areas of the piston circumference in which the gaps arise, additional elements are introduced which, for. B. spread the seal accordingly or press on resiliently.

Since the invention creates a reciprocating compressor that has very high pressure and delivery rates with the simplest construction, even with small sizes, such a reciprocating compressor is, as already mentioned, particularly suitable for a portable breakdown assistance system for sealing and pumping up inflatable objects, in particular Tires, wherein the breakdown assistance system includes a container for an automatic sealant that can be filled into the inflatable object, a valve and distributor unit for sealant and compressed gas and connection means between the valve and distributor unit and the inflatable object, means for supplying energy and switching and / or control devices for the Includes operation of the system and is equipped with a pressurized gas source in the form of a compressor.

Fig. 1

eine Prinzipskizze eines erfindungsgemäßen Hubkolbenverdichters

Fig. 2

eine Fertigungszeichnung eines Kolbens für einen erfindungsgemäßen Hubkolbenverdichter.

The innovation is to be explained in more detail using an exemplary embodiment. Show it

Fig. 1

a schematic diagram of a reciprocating compressor according to the invention

Fig. 2

a production drawing of a piston for a reciprocating compressor according to the invention.

the Fig. 1 shows in the form of a schematic diagram a reciprocating compressor 1 of a portable breakdown assistance system for sealing and inflating tires with a piston 3 driven by a slider crank drive and a piston 3 that is movable back and forth in a cylinder 2 and sealed against the cylinder wall, the slider crank drive being a piston 3 arranged on a crankshaft Crank wheel 4 with an eccentric crank pin 5 and a connecting rod 6 arranged between the piston 3 and the crank pin 5, the piston 3 or piston head 7 being arranged stationary perpendicular to the connecting rod axis 8, so that the connecting rod axis 8 and piston axis 9 match. The right part of the Fig. 1 shows the reciprocating compressor 1 with its piston 3 in TDC, the left part shows the reciprocating compressor 1 with its piston 3 during the compression stroke.

With the rigid connection between the piston and the connecting rod without a piston joint, the highest sealing ability between the piston and cylinder in TDC and BDC is achieved, as on the right-hand side of the Fig. 1 shown in the OT.

In the middle of the range of motion, the sealing ability normally decreases, because a deviation of the symmetry axis of the piston, i.e. in this case the connecting rod and piston axis 8, 9 from the symmetry axis of the cylinder 10, the so-called piston inclination is expressed and the piston seal does not fit optimally the cylinder wall is given more.

mm und die kleine Halbachse 15 eine Länge von $\left(\frac{\mathrm{31,7}}{2}\right)$

mm auf.The one in the Fig. 1 This is not the case, since the piston, understood here as an entire assembly with a piston seal, is designed so that the piston compressor 1 according to the invention shown is not the case during the on the left side of the Fig. 1 Compression stroke illustrated by the relative inclination between the piston axis and the cylinder axis, the sickle-shaped gaps 11, 12 between the piston edge and the cylinder wall can be sealed, namely in that the piston 3 and thus the piston head 7 has an oval-elliptical shape deviating from the circular shape, through which the sickle-shaped Column are at least partially compensable. The projection 7a of the inclined piston head 7 in the lower left part of the Fig. 1 shows this by showing the deviations 11a and 12a of the piston head 7 from the ideal circular shape13. The large semi-axis 14 of the oval-elliptical piston head has a length of $\left(\frac{32.1}{2}\right)$

mm and the small semi-axis 15 has a length of $\left(\frac{31.7}{2}\right)$

mm on.

The annular piston seal, not shown here, is designed so compressible and geometrically flexible that a secure elastic seal takes place between the piston and the cylinder wall during the entire stroke movement and in the dead centers. Of course, the seal is then compressed and deformed more strongly in TDC and BDC than in the middle compression range.

Fig. 2 shows a production drawing of a piston 3 for a reciprocating compressor according to the invention in a sectional view and in a plan view with one of the Circular shape deviating oval-elliptical shape, where the diameter X corresponds to twice the major semi-axis 14 and the diameter Y corresponds to twice the small semi-axis 15, here X = 32.1mm and Y = 31.7mm.

The piston is provided with kidney-shaped recesses 16 and 17, which give the piston sufficient flexibility in the area of the large semiaxes thanks to the circumferential webs 18 and 19 serving as resilient elements, so that the piston can approximate the ideal circular shape in TDC and BDC .

The sickle-shaped gaps are compensated here by resilient elements on the piston, the resilient elements being formed in the piston body, here by means of resilient circumferential webs 18, 19, which are formed by kidney-shaped recesses 16, 17 that are concave towards the center of the piston, with webs and recesses are arranged over a partial circumference of the piston 3 in the area of the large semi-axes.

List of reference symbols (Part of the description)

1

Reciprocating compressors

2

cylinder

3

Pistons

4th

Crank wheel

5

Crank pin

6th

Connecting rod

7th

Piston crown

7a

Projection of the inclined piston crown

8th

Connecting rod axis

9

Piston axis

10

Axis of symmetry of the cylinder

11

Sickle-shaped gap

11a

Deviation from the circular shape

12th

Sickle-shaped gap

12a

Deviation from the circular shape

13th

Ideal circular shape

14th

Major semi-axis

15th

Small semi-axis

16

Kidney-shaped recess

17th

Kidney-shaped recess

18th

Circumferential web

19th

Circumferential web

Claims (9)

1. Reciprocating-piston compressor (1) having a piston (3) which is driven by means of a slider-crank mechanism and having a piston (3) which is movable in reciprocating fashion in a cylinder (2) and which is sealed off with respect to the cylinder wall, wherein the slider-crank mechanism has a crank wheel (4) which is arranged on a crankshaft and which has an eccentric crankpin (5), and also a connecting rod (6) which is arranged between the piston (3) and the crankpin (5), wherein the piston (3) or piston crown (7) is arranged so as to be static and perpendicular with respect to the connecting-rod axis (8), wherein the piston (3) and/or the cylinder (2) are/is designed such that the sickle-shaped gaps (11, 12) that arise between piston edge and cylinder wall during the respective stroke movement owing to the relative inclination between piston axis (9) and cylinder axis (10) can be sealed off, wherein the piston as an overall assembly with a piston seal has an oval-elliptical shape which deviates from the circular shape, characterized in that the piston (3) is a circular shape and the piston seal is ring-shaped and has a varying thickness, in which the thickness maximum is arranged and designed such that the sickle-shaped gaps (11, 12) can be compensated, with the result that an elastic seal between piston and cylinder wall is effected during the entire stroke movement and at the dead centres.
2. Reciprocating-piston compressor according to Claim 1, in which the piston has an oval-elliptical shape, in which the length of the semi-minor axis (15) is at least 80% of the length of the semi-major axis (14).
3. Reciprocating-piston compressor according to Claim 2, in which the piston has an oval-elliptical shape, the semi-major axis (14) of which has a length of $\left(\frac{3.1}{2}\right)$

   

   mm and the semi-minor axis (15) of which has a length of $\left(\frac{3.7}{2}\right)$

   

   mm.
4. Reciprocating-piston compressor according to one of Claims 1 to 3, in which the cylinder has, in its central compression region, an oval-elliptical shape which deviates from the circular shape and by way of which the sickle-shaped gaps (11, 12) can be at least partially compensated, with the result that an elastic seal between piston and cylinder wall is effected during the entire stroke movement and at the dead centres.
5. Reciprocating-piston compressor according to one of Claims 1 to 4, in which the sickle-shaped gaps (11, 12) on the piston (3) or/or on the seal are compensated by resilient elements (18, 19).
6. Reciprocating-piston compressor according to Claim 5, in which the resilient elements are formed in the piston body, in particular by means of resilient circumferential webs (18, 19) which are formed over a partial circumference of the piston (3) by kidney-shaped cutouts (16, 17) which are arranged in a concave manner towards the centre of the piston.
7. Reciprocating-piston compressor according to one of Claims 1 to 6, in which the sickle-shaped gaps (11, 12) on the piston (3) or/or on the seal are compensated by actuating elements, in particular by elements that are impinged on by a pressure medium.
8. Reciprocating-piston compressor according to one of Claims 1 to 7, in which the sickle-shaped gaps (11, 12) on the piston (3) or/or on the seal are compensated by inserted shaped elements.
9. Portable breakdown assistance system for sealing and inflating inflatable articles, in particular tyres, wherein the breakdown assistance system comprises a container for an automatic sealant that can be filled into the inflatable article, a valve and distributor unit for sealant and pressurized gas, and connecting means between the valve and distributor unit and the inflatable article, means for supplying energy, and also switching and/or control devices for the operation of the system, and is equipped with a pressurized-gas source in the form of a compressor, designed as a reciprocating-piston compressor according to one of Claims 1 to 8.

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