WO2019081240A1 - PISTON COMPRESSOR - Google Patents

Abstract

Piston compressor (1) for compressing a working fluid, in particular a liquid or gaseous fuel, comprising a piston (4) which can reciprocate in a bore (2) of a cylinder (3) and which can be filled with the working fluid within the bore (2) Compression space (5) limited. In the piston (4) at least one annular pressure chamber (6) is formed, which is hydraulically connected to the compression space (5) and radially outside by an elastically deformable wall portion or an elastically deformable membrane (7) is fluid-tight.

Description

 description

Title:

 Piston compressor The invention relates to a piston compressor for compressing a working fluid having the features of the preamble of claim 1.

In particular, the working fluid may be a liquid or gaseous fuel, such as natural gas ("NG"). When the natural gas is used to power an internal combustion engine of a motor vehicle, it will be aboard the vehicle

It is usually carried in a tank in liquid form ("liquefied natural gas" = LNG) Before the natural gas is blown into a combustion chamber of the internal combustion engine, it is compressed, and this shows a preferred application of the presently proposed piston compressor.

In addition, the proposed reciprocating compressor can be used for compressing any gaseous and / or liquid media, so that the presently selected term "piston compressor" also includes piston pumps

From WO 2003/010446 AI, for example, a piston compressor for the compression of a cooling gas emerges, which comprises a cylinder and a reciprocating piston in the cylinder. The cylinder and piston define a compression chamber. The piston is connected to a drive mechanism, wherein the

Connection via pins, which are received in radial holes of the piston. Since the radial holes are hydraulically connected to the compression chamber via a radial gap remaining between the piston and the cylinder, it is necessary to seal the radial holes. The seal is made via in the radial holes recorded Sealing elements. In this way, a leakage of the cooling gas through the radial holes is counteracted.

The present invention has for its object to provide a reciprocating compressor, which has an improved efficiency. To achieve this, the leakage in the region of an annular gap between the piston and the cylinder of the reciprocating compressor should be minimized. The reciprocating compressor is thus designed to compress a liquid or gaseous fuel, such as natural gas, to high pressure (preferably about 600 bar).

To solve the problem of the reciprocating compressor with the features of

Proposed claim 1. Advantageous developments of the invention can be found in the dependent claims.

Disclosure of the invention

The piston compressor proposed for compressing a working fluid, in particular a liquid or gaseous fuel, comprises a piston which can be moved back and forth in a bore of a cylinder and which delimits within the bore a compression space which can be filled with the working fluid. According to the invention at least one annular pressure chamber is formed in the piston, which is hydraulically connected to the compression space and radially outwardly fluid-tightly closed by an elastically deformable wall portion or an elastically deformable membrane.

The stroke of the piston causes compression of the trapped working fluid in the compression space. This means that the pressure in the compression chamber increases. At the same time, the pressure in the piston formed in the annular pressure chamber increases, since it is hydraulically connected to the compression chamber. In contrast, the pressure in an annular gap remaining between the piston and the cylinder does not increase or does not increase in the same way, so that due to the pressure difference, the elastically deformable wall section or the elastically deformable membrane becomes more heavily loaded on the inside and deforms. Since the pressure in the pressure chamber is greater than in the annular gap, the wall portion or arched bulges Membrane radially outward and narrowed in this way the annular gap. The annular gap is minimized in this way and the leakage is reduced.

The deformation of the wall section or the membrane is proportional to the pressure rise in the pressure chamber. This means that as the pressure increases, so does the deformation. The desired effect of gap minimization is thus given over the entire pressure range.

Since there is an approximately linear pressure drop in the annular gap between the piston and the cylinder, the pressure in the pressure chamber is always greater than the pressure in the annular gap.

By means of the pressure-dependent gap minimization, the leakage over the annular gap from the compression space during operation of the reciprocating compressor can be significantly reduced. This means that the losses due to leakage are minimal, so that the reciprocating compressor has a high efficiency.

Furthermore, production-related diameter tolerances can be compensated by means of the pressure-dependent gap minimization, so that the production of the reciprocating compressor is simplified.

According to a preferred embodiment of the invention, the annular pressure chamber is hydraulically connected via at least one channel formed in the piston with the compression space. The channel is to be dimensioned such that it allows a fast filling and thus a rapid pressure build-up in the pressure chamber. Preferably, several, for example, four to eight channels for the hydraulic connection of the pressure chamber with the compression space are provided. In this way, the filling of the pressure chamber can be further accelerated. In addition, a uniform filling of the pressure chamber is ensured.

In order to keep the dead volume small, the at least one channel should be designed to be as short as possible to the hydraulic connection of the pressure chamber with the compression space. This can be effected in that the annular pressure chamber is formed in the region of the end of the piston facing the compression space. Furthermore, it is proposed that the at least one channel for the hydraulic connection of the pressure chamber to the compression space be designed as an oblique bore, which extends from a compression space bounding the end face of the piston to the pressure chamber. The design as an oblique hole, the length of the channel can be further reduced. Furthermore, a crop-free and thus flow-optimized hydraulic connection can be realized which leads from the compression chamber directly into the pressure chamber.

The annular pressure chamber can be formed by a cavity enclosed in the piston on all sides. For this purpose, the piston has preferably been produced in an additive production process, in particular in a 3D printing process. The formation of the pressure chamber as a cavity enclosed on all sides simplifies the manufacture of the reciprocating compressor, since the number of components remains unchanged. This means that no additional assembly steps are required to realize the piston compressor according to the invention. Furthermore, sealing measures can be omitted in order to carry out the annular pressure chamber in a fluid-tight manner.

Preferably, the annular pressure chamber is arranged concentrically with respect to the piston and has circumferentially the same width. In the case of a designed as a cavity in the piston pressure chamber, which is bounded radially outwardly by an elastically deformable wall portion of the piston, it is ensured in this way that the wall portion circumferentially has a constant thickness. This means that the wall section deforms uniformly over its outer circumference.

Alternatively, the annular pressure chamber may be formed by a circumferential circumferential groove disposed on the outer peripheral side into which the diaphragm is inserted to close the pressure chamber to the outside. The annular groove can be inexpensively manufactured in a machining process, so that the piston need not be manufactured in an additive manufacturing process. Rather, a conventional piston can be taken and reworked. The membrane is preferably inserted flush with an outer peripheral surface of the piston in the annular groove, so that the deformation of the membrane causes a maximum gap narrowing. Advantageously, the annular groove is stepped, so that the pressure chamber is bounded on both sides by a shoulder for installation and / or attachment of the membrane. The paragraph allows in particular a flush mounting of the membrane. In the radial direction, therefore, preferably the shoulder and the membrane have the same

Dimension on. This means that preferably the heel height corresponds to the membrane thickness.

To produce a fluid-tight connection, it is proposed that the membrane be welded or glued to the piston. The welding or adhesive seams can be performed circumferentially, so that over this an effective over the circumference of the piston sealing the pressure chamber can be achieved. According to a preferred embodiment, the membrane is welded by means of two round seams with the piston.

The membrane is preferably made of a metal sheet or of a metal tube. The metal sheet must first be bent into a ring and welded longitudinally, whereby the welding can be done on the piston. The metal tube is preferably a seamlessly drawn tube, which can be mounted on the piston and then welded by means of two round seams with the piston. In order to facilitate the mounting of the metal tube, the piston may be reduced at its end facing the compression space to the tube inner diameter.

Furthermore, it is proposed that the compression space can be connected via an inlet valve to a fluid supply and / or via an outlet valve to a pressure line. The working fluid enters the compression chamber via the inlet valve, where it is compressed by means of the piston stroke. The compressed working fluid can then be supplied via the outlet valve and the subsequent pressure line to a fluid reservoir, which is preferably a Hochdruckspei- rather for a liquid or gaseous fuel, such as natural gas, is injected under high pressure in the combustion chamber of an internal combustion engine becomes. Because of the reduced leakage over the remaining between the piston and the cylinder annular gap high pressures in the compression chamber can be achieved be enough, so that the proposed piston compressor is particularly suitable as LNG compressor for mobile application in a motor vehicle.

Preferred embodiments of the invention are explained below with reference to the accompanying drawings. These show:

1 shows a schematic sectional view of a piston compressor according to the invention according to a first preferred embodiment, FIG. 2 shows a schematic longitudinal section through a piston compressor according to the invention according to a second preferred embodiment,

3 in an enlarged section of FIG. 2 in the region of the channel and the pressure chamber,

4 a) -c) in each case an enlarged detail of FIG. 3 in the region of the pressure chamber with undeformed and differently strongly deformed membrane, FIG.

Fig. 5 a) and b) are each a side view of the piston of the piston compressor of the invention of FIG. 2 with undeformed and deformed membrane, and

Fig. 6 is a longitudinal section through the piston of Fig. 5 in the region of the pressure chamber (without membrane). Detailed description of the drawings

The piston compressor 1 according to the invention shown in FIG. 1 comprises a cylinder 3 with a bore 2, in which a piston 4 is reciprocally accommodated (see arrow 18). The piston 4 delimits within the bore 2 a compression space 5, which can be connected via an inlet valve 12 to a fluid supply 13 or filled with a working medium. After the working fluid in the compression chamber 5 has been compressed by a stroke of the piston 4, it can be fed via an outlet valve 14 to a pressure line 15. To the pressure line 15, a fluid reservoir (not shown) may be connected. In order to reduce the leakage via an annular gap 16 which remains between the piston 4 and the cylinder 3, the piston 4 has an annular cavity which forms a pressure chamber 6 (indicated by dashed lines in FIG. 1). The pressure chamber 6 is closed to the outside by an elastically deformable wall portion of the piston 4, which bulges outwardly at a pressure increase in the pressure chamber 6 and the annular gap 16 closes. The pressure increase in the pressure chamber 6 is effected by the fact that the pressure chamber 6 is hydraulically connected to the compression space 5. That is, in a stroke of the piston 4 not only the pressure in the compression chamber 5, but also the pressure in the pressure chamber 6 increases. In contrast, the pressure in the annular gap 16 drops, so that the desired deformation of the piston wall section is achieved via the pressure difference.

In order to produce the serving as a pressure chamber 6 annular cavity in the piston 4, this has been made additive in a 3 D printing process.

FIGS. 2 and 3 show a further embodiment of a reciprocating compressor 1 according to the invention. Here, the pressure chamber 6 is formed by an outer circumferential side formed in the piston 4 annular groove which is closed in a fluid-tight manner via a flush-mounted in the annular groove 7 membrane. Via channels 8, which are designed as inclined bores, the pressure chamber 6 is hydraulically connected to the compression chamber 5. For this purpose, the oblique bores are guided by the pressure chamber 6 up to an end face 9 of the piston 4, which delimits the compression space 5.

As can be seen in particular from FIGS. 4a-4c, the annular groove formed on the outer peripheral side in the piston 4 is stepped, so that flat shoulders 11 are formed on both sides. The paragraphs 11 are used to create the membrane 7, which can thus be flush-fitted with an outer peripheral surface 10 of the piston 4 in the annular groove. Via welds 17, which are designed as round seams, the membrane 7 is fluid-tightly connected to the piston 4.

If essentially the same pressure prevails in the pressure chamber 6 and in the annular gap 16, the diaphragm 7 is pressure-balanced. This means that they - as in Fig. 4a shown - is undeformed and has the shape of a simple hollow cylinder. However, if the pressure in the pressure chamber 6 increases, so that the pressure in the pressure chamber 6 is higher than in the annular gap 16, the diaphragm 7 deforms into the annular gap 16 so that it - as shown by way of example in FIG. 4b - minimizes becomes. In Fig. 4b, the membrane 7 comes to rest on the cylinder 3, so that an optimal seal is achieved. In Fig. 4c, the deformation of the membrane 7 is shown exaggerated. Such a strong diaphragm 7 could deform only if they did not come to rest on the cylinder 3.

Figures 5a and 5b show the piston of the reciprocating compressor of Figures 2 and 3 and 4a to 4c respectively in a side view. In Fig. 5a, the diaphragm 7 is pressure balanced, that is not deformed. In Fig. 5b, the piston 4 is shown with deformed membrane 7.

FIG. 6 shows an example of a preferred geometry of an annular groove formed in the piston 4, the piston 4 having an outer diameter of 30 mm. The annular groove has a depth Ti = 0.8 mm and a height Hi = 4 mm in a first pressure chamber 6 forming region. In the area of the paragraphs 11, the annular groove has a depth T2 = 0.2 mm and a height H2 = 6 mm. At its base, the annular groove is rounded, with the radius R = 0.45 mm. The serving as a channel 8, opening into the annular groove oblique bore has a diameter of 1 mm.

The annular groove shown in Fig. 6 is preferably closed by a membrane 7, which has a thickness of 0.2 mm and a height of 6 mm, so that it is flush with the outer peripheral surface 10 of the piston 4 inserted into the annular groove. The distance of the annular groove from the end face 9 of the piston 4 is preferably 4 mm.

Claims

claims Compressor (1) for compressing a working fluid, in particular a liquid or gaseous fuel, comprising a in a bore (2) of a cylinder (3) reciprocally movable piston (4) within the bore (2) one with the Working fluid fillable compression chamber (5) limited characterized in that in the piston (4) at least one annular pressure chamber (6) is formed, which is hydraulically connected to the compression space (5) and radially outwardly by an elastically deformable wall portion or an elastically deformable membrane (7) fluid-tight. 2. piston compressor (1) according to claim 1, characterized in that the annular pressure chamber (6) via at least one in the piston (4) formed channel (8) with the compression chamber (5) is hydraulically connected, wherein preferably the channel (8) is designed as an oblique bore extending from one of Compression space (5) limiting end face (9) of the piston (4) to the pressure chamber (6). 3. piston compressor (1) according to claim 1 or 2, characterized in that the annular pressure chamber (6) is formed by a cavity enclosed on all sides in the piston (4), which has preferably been produced in an additive manufacturing process, in particular in a 3 D printing process. 4. piston compressor (1) according to one of the preceding claims, characterized in that the annular pressure chamber (6) is arranged concentrically in train on the piston (4) and circumferentially has the same width. 5. piston compressor (1) according to any one of the preceding claims, characterized in that the annular pressure chamber (6) is formed by an outer peripheral circumferential groove, in which the membrane (7) is preferably flush with an outer peripheral surface (10) of the piston (4) is inserted. 6. piston compressor (1) according to claim 5, characterized in that the annular groove is stepped, so that the pressure chamber (6) on both sides of a paragraph (11) for conditioning and / or attachment of the Membrane (7) is limited. 7. reciprocating compressor (1) according to one of the preceding claims, characterized in that the membrane (7) fluid-tight with the piston (4) connected, preferably welded or glued, is. 8. piston compressor (1) according to one of the preceding claims, characterized in that the membrane (7) is made of a metal sheet or a metal tube. 9. reciprocating compressor (1) according to one of the preceding claims, characterized in that the compression space (5) via an inlet valve (12) with a fluid supply (13) and / or via an outlet valve (14) with a pressure line (15) is connectable.