DOUBLE-PISTON COMPRESSOR OF A COMPRESSED AIR SUPPLY DEVICE

A double-piston compressor of a compressed air supply device. The double-piston compressor includes a low pressure stage and a high pressure stage, each of the low pressure stage and the high pressure stage having a cylinder with a piston guided in an axially movable manner therein. A piston of the cylinder of the low pressure stage and a piston of the cylinder of the high pressure stage are drivingly connected to the drive shaft via a sliding block guide. Sliding block tracks of the sliding block guide are constructed and arranged such that, during operation of the double-piston compressor, a movement of the pistons follows a stroke curve that deviates from a regular sinusoidal stroke curve, which has an amplitude corresponding to an eccentricity of the drive element.

FIELD

The invention relates to a double-piston compressor of a compressed air supply device.

BACKGROUND

Double-piston compressors having two pistons which are rigidly connected to one another via a piston rod and are guided in an axially movable manner in cylinders arranged radially opposite with respect to the axis of rotation of a drive shaft have long been known in embodiments which differ in terms of their drive technology.

In one type of double-piston compressor which is known for example from DE 103 21 771 B4, the piston rod is drivingly connected to the drive shaft via a con rod. The con rod is connected in an articulated manner to the drive shaft and the piston rod, on the one hand via a crank pin, which engages in a first end-side bore and is secured eccentrically on the drive shaft, and on the other hand via a drive pin which engages in a second end-side bore and is secured off-center on the piston rod.

In contrast, in a substantially simpler and more space-saving design of a double-piston compressor, the piston rod is drivingly connected to the drive shaft merely via a sliding block guide. The sliding block guide comprises a recess, which is constructed in the piston rod, is provided with two parallel sliding block tracks and is aligned perpendicularly to the axis of rotation of the drive shaft, and a drive element, which is in engagement with the recess and is eccentrically secured on the drive shaft such that it is axially parallel with respect to the axis of rotation of the drive shaft. Depending on the resultant force direction of the pressure forces acting on the two pistons, the drive element abuts against one of the two sliding block tracks and, bridging the clearance which is inevitably present in the sliding block guide, moves to abut against the other sliding block track when the resultant force direction is reversed. The recess in the piston rod can be constructed in a U shape, as is known for example from DE 918 042 B. In this case, the side walls of the recess form the parallel sliding block tracks and the two parts of the piston rod are connected to one another via the base wall of the recess.

As an alternative to this, the recess can be constructed as a slot-shaped through opening, as is known for example from FIG. 8 of DE 44 33 068 C2 and DE 10 2012 223 114 A1. In this case, the side walls of the recess form the parallel sliding block tracks. To connect the two parts of the piston rod, end-side webs are required in this embodiment of the sliding block guide, which are usually designed in the shape of a circular arc but, with an appropriate spacing, can also be designed linearly. The drive element can be a crank pin, which is eccentrically secured on the drive shaft such that it is axially parallel with respect to the axis of rotation of the drive shaft and which, as is known for example from FIG. 8 of DE 44 33 068 C2, is guided in a directly slideable manner on the parallel sliding block tracks of the sliding block guide.

To reduce the driving resistance and the wear on the sliding block tracks, the driving element can, as is known for example from DE 918 042 B, DE 1 932 737 U and DE 197 15 291 C2, also be constructed as the outer ring of a rolling bearing, which is arranged on a crank pin eccentrically secured on the drive shaft and whereof the outer ring is guided in a rollable manner on the sliding block tracks of the sliding block guide.

In contrast, EP 0 389 414 B1 describes a relatively large reciprocating compressor provided for stationary use, having four cylinders which are radially opposite in pairs and pistons which are connected to one another, in which an externally substantially rectangular sliding body in each case is mounted on a crank pin, which is eccentrically secured on the drive shaft, such that it is rotatable with relatively low resistance via a rolling bearing, and is guided in a rollingly displaceable manner between sliding block tracks of the sliding block guide via a linear guide having a rolling body.

Common to the known types of double-piston compressors having sliding block guides is that the two parallel sliding block tracks are of a planar design and are aligned perpendicularly to the longitudinal axis of the piston rod. This construction and arrangement of the sliding block tracks inevitably results in a regular sinusoidal stroke curve of the pistons with an amplitude corresponding to the eccentricity of the crank pin.

SUMMARY

In an embodiment, the present invention provides a double-piston compressor of a compressed air supply device. The double-piston compressor includes a low pressure stage and a high pressure stage, each of the low pressure stage and the high pressure stage having a cylinder with a piston guided in an axially movable manner therein. The cylinder of the low pressure stage and the cylinder of the high pressure stage are arranged radially opposite with respect to an axis of rotation of a drive shaft. The piston of the cylinder of the low pressure stage and the piston of the cylinder of the high pressure stage are rigidly connected to one another by a piston rod. The piston of the cylinder of the low pressure stage and the piston of the cylinder of the high pressure stage are drivingly connected to the drive shaft via a sliding block guide. The sliding block guide has a recess which is arranged in the piston rod, is provided with two parallel sliding block tracks, and is aligned perpendicularly to the axis of rotation of the drive shaft. The sliding block guide has a drive element in engagement with the recess, arranged axially parallel with respect to the axis of rotation of the drive shaft, and secured on the drive shaft with an eccentricity. The sliding block tracks of the sliding block guide are constructed and arranged such that, during operation of the double-piston compressor, a movement of the pistons follows a stroke curve that deviates from a regular sinusoidal stroke curve, which has an amplitude corresponding to the eccentricity of the drive element.

DETAILED DESCRIPTION

Embodiments of the present invention provide a double-piston compressor of a compressed air supply device, having a low pressure stage and a high pressure stage, which each have a cylinder with a piston guided in an axially movable manner therein, wherein the two cylinders are arranged radially opposite with respect to an axis of rotation of a drive shaft, wherein the two pistons are rigidly connected to one another by means of a piston rod, wherein the two pistons are drivingly connected to the drive shaft via a sliding block guide, wherein the sliding block guide has a recess which is arranged in the piston rod, is provided with two parallel sliding block tracks and is aligned perpendicularly to the axis of rotation of the drive shaft, and in which the sliding block guide has a drive element which is in engagement with the recess, is arranged axially parallel with respect to the axis of rotation of the drive shaft and is secured on the drive shaft with an eccentricity.

Embodiments of the present invention provide a double-piston compressor having a sliding block guide of the type mentioned at the outset, which has two parallel sliding block tracks.

A regular sinusoidal stroke curve of pistons can be modified in a desired manner by a suitable alteration to the alignment and/or the contour of the parallel sliding block tracks of the sliding block guide.

Embodiments of the invention therefore provide a double-piston compressor of a compressed air supply device, which has a low pressure stage and a high pressure stage. The two pressure stages each have a cylinder with a piston guided in an axially movable manner therein, wherein the two cylinders are arranged radially opposite with respect to an axis of rotation of a drive shaft. The two pistons are rigidly connected to one another by means of a piston rod and are drivingly connected to the drive shaft via a sliding block guide. The sliding block guide has a recess which is arranged in the piston rod, is provided with two parallel sliding block tracks and is aligned perpendicularly to the axis of rotation of the drive shaft. Moreover, the sliding block guide has a drive element which is in engagement with the recess in the piston rod, is arranged axially parallel with respect to the axis of rotation of the drive shaft and is secured on the drive shaft with an eccentricity.

According to embodiments of the invention, the sliding block tracks of the sliding block guide are constructed and arranged such that, during operation of the double-piston compressor, the movement of the pistons follows a stroke curve which deviates from a regular sinusoidal stroke curve, which has an amplitude corresponding to the eccentricity of the drive element.

A first modification of the sliding block guide provides that the sliding block tracks of the sliding block guide are arranged at an inclination in the direction of rotation of the drive shaft relative to a perpendicular on a longitudinal axis of the piston rod. It is thus achieved that the stroke curve of the pistons is phase-shifted towards late and that the amplitude of the stroke curve is increased beyond the eccentricity of the drive element. In contrast, the stroke width, i.e. the angle of rotation range of the intake and pressure strokes of the pistons, remains unaltered.

An alternative second modification of the sliding block guide provides that the sliding block tracks of the sliding block guide are arranged at an inclination in opposition to the direction of rotation of the drive shaft relative to the perpendicular on the longitudinal axis of the piston rod. It is thus achieved that the stroke curve of the pistons is phase-shifted towards early and that the amplitude of the stroke curve is increased beyond the eccentricity of the drive element. The stroke width of the intake and pressure strokes of the pistons also remains unaltered in this case.

For functional reasons, the angle of inclination of the sliding block tracks relative to the perpendicular on the longitudinal axis of the piston rod, should be a maximum of 45°.

A third modification of the sliding block guide, which can be applied both to a perpendicular and an inclined alignment of the sliding block tracks, provides that at least one of the sliding block tracks of the sliding block guide has a circular-arc-shaped indentation in a central portion. As a result of the indentation, the peak of the stroke curve is capped, or the maximum amplitude is reduced, and the pressure stroke of the piston facing the indentation and the intake stroke of the piston facing away from the indentation are therefore reduced accordingly.

The radius and the depth of the circular-arc-shaped indentation of the at least one sliding block track are dimensioned such that the stroke height of the piston rod when the drive element passes through the indentation is kept constant. With such a geometry of the indentation, it is ensured that the piston rod is not displaced when the drive element passes through the indentation, so that the progression of the stroke curve of the pistons in the relevant portion is linear and not wavy.

A fourth modification of the sliding block guide, which can be applied both to a perpendicular alignment of the sliding block tracks and in combination with the above-mentioned modifications of the sliding block guide, provides that the sliding block tracks of the sliding block guide are curved in the shape of a circular arc in the direction of one of the two pistons. As a result of this modification of the sliding block guide, the stroke width, i.e. the angle of rotation range of the piston rod, during the stroke movement is increased in the direction of the cylinder facing the curvature of the sliding block tracks and the stroke width of the piston rod during the stroke movement is reduced by the same amount in the direction of the cylinder facing away from the curvature of the sliding block tracks.

An embodiment, known per se, of a double-piston compressor1.5of a compressed air supply device is shown inFIG. 5in a schematic cross-sectional view. The double-piston compressor1.5has a low pressure stage2and a high pressure stage3which each comprise a cylinder4,6with a piston5,7guided in an axially movable manner therein. The two cylinders4,6are arranged radially opposite in a housing with respect to an axis of rotation11of a drive shaft10. The two pistons5,7are rigidly connected to one another via a piston rod8and are drivingly connected to the drive shaft10via a sliding block guide14.5. The sliding block guide14.5comprises a recess15, which is constructed in the piston rod8, is provided with two parallel sliding block tracks16,17and is aligned perpendicularly to the axis of rotation11of the drive shaft10, and a drive element12which is in engagement with the recess15and is eccentrically secured on the drive shaft10such that it is axially parallel with respect to the axis of rotation11of the drive shaft10. The two sliding block guides16,17here are aligned perpendicularly to a longitudinal axis9of the piston rod8. By way of example, the drive element12is formed by a crank pin13which is secured on the drive shaft10such that it is radially spaced from the axis of rotation11by the amount of an eccentricity e and is guided in a directly slideable manner on the parallel sliding block tracks16,17of the sliding block guide14.5.

InFIG. 5a, a stroke curve ZH(ϕ)_1.5illustrates the movement of the pistons5,7or the piston rod8of the known double-piston compressor1.5during a revolution of the drive shaft10. The angle of rotation of the drive shaft10here is denoted by ϕ, the direction of rotation of the drive shaft10is assumed to be clockwise according to the direction of rotation arrow18shown inFIG. 5, the 0° position of the drive shaft10or the crank pin13corresponds to the position shown inFIG. 5, the stroke height of the pistons5,7is denoted by ZHand the stroke direction of the pistons5,7is assumed to be positive according to the stroke direction arrow19, shown inFIG. 5, in the direction of the cylinder6of the high pressure stage3. The stroke curve ZH(ϕ) of the pistons5,7, which is shown in the graph ofFIG. 5a, has a regular sinusoidal progression with the amplitude which corresponds to the eccentricity e of the crank pin13. The progression of this stroke curve can then be expressed as ZH(ϕ)=e*sin(ϕ).

FIG. 1illustrates a double-piston compressor1.1of a compressed air supply device according to a first embodiment in a schematic cross-sectional view, which differs from the embodiment of the double-piston compressor1.5according toFIG. 5due to an altered arrangement of the sliding block guide14.1. In this case, the recess15with the two parallel sliding block tracks16,17is arranged pivoted relative to a perpendicular20located on the longitudinal axis9of the piston rod8through an angle of inclination of α=25° here in the direction of rotation18of the drive shaft10.

The stroke curve ZH(ϕ)_1.1, shown in the graph ofFIG. 1a, of the pistons5,7or the piston rod8of the double-piston compressor1.1likewise has a regular sinusoidal progression. However, owing to the inclined arrangement of the sliding block tracks16,17in the direction of rotation18of the drive shaft10, the stroke curve ZH(ϕ)_1.1has a phase shift towards late and a stroke height exceeding the eccentricity e of the crank pin13. The progression of the stroke curve ZH(ϕ)_1.1of the pistons5,7of the double-piston compressor1.1can be expressed by the formula ZH(ϕ)=e*(sin(ϕ)−cos(ϕ)*tan(∝)). For comparison, inFIG. 1, the stroke curve ZH(ϕ)_1.5of the pistons5,7of the double-piston compressor1.5according toFIG. 5is also shown as a dot-and-dash curve.

FIG. 2illustrates a double-piston compressor1.2of a compressed air supply device according to a second embodiment of the invention in a schematic cross-sectional view, which differs from the embodiment of the double-piston compressor1.5according toFIG. 5due to a differently altered arrangement of the sliding block guide14.2. The recess15with the two parallel sliding block tracks16,17is now arranged pivoted relative to the perpendicular20located on the longitudinal axis9of the piston rod8through an angle of inclination of α=−25° here in opposition to the direction of rotation18of the drive shaft10.

The stroke curve ZH(ϕ)_1.2, shown in the graph ofFIG. 2a, of the pistons5,7or the piston rod8of the double-piston compressor1.2in turn has a regular sinusoidal progression which, owing to the inclined arrangement of the sliding block tracks16,17in opposition to the direction of rotation18of the drive shaft10, now has a phase shift towards early and likewise a stroke height exceeding the eccentricity e of the crank pin13. Taking the minus sign of the angle of inclination a into account, the progression of the stroke curve ZH(ϕ)_1.2of the pistons5,7of the double-piston compressor1.2can likewise be expressed by the formula ZH(ϕ)=e*(sin(ϕ)−cos(ϕ)*tan(∝)), For comparison, inFIG. 2, the stroke curve ZH(ϕ)_1.5of the pistons5,7of the double-piston compressor1.5according toFIG. 5is also shown as a dot-and-dash curve.

FIG. 3illustrates a double-piston compressor1.3of a compressed air supply device according to a third embodiment of the invention in a schematic cross-sectional view, which differs from the embodiment of the double-piston compressor1.5according toFIG. 5due to a geometrically altered construction of the sliding block guide14.3. By way of example, the sliding block track16′ of the sliding block guide14.3which faces the piston5of the lower pressure stage2now has, in the region of the recess15′, a circular-arc-shaped indentation21in a central portion. The radius and the depth of the circular-arc-shaped indentation21are dimensioned such that the stroke height ZHof the piston rod8when the crank pin13passes through the indentation21is held constant.

In the first half-section of 0° to 180°, which forms the intake stroke of the piston5of the low pressure stage2and the pressure stroke of the piston7of the high pressure stage3, the stroke curve ZH(ϕ)_1.3, shown in the graph ofFIG. 3a, of the pistons5,7or the piston rod8is identical to the stroke curve ZH(ϕ)_1.5of the pistons5,7of the double-piston compressor1.5according toFIG. 5. In contrast, in the second half-section of the stroke curve ZH(ϕ)_1.3of >180° to <360° , which forms the pressure stroke of the piston5of the low pressure stage2and the intake stroke of the piston7of the high pressure stage3, the peak of the stroke curve ZH(ϕ)_1.3is capped, so that the pressure stroke of the piston5of the low pressure stage2and the intake stroke of the piston7of the high pressure stage3are reduced in relation to the stroke height produced by the eccentricity3of the crank pin in the double-piston compressor1.5according toFIG. 5. For comparison, inFIG. 3, the stroke curve ZH(ϕ)_1.5of the pistons5,7of the double-piston compressor1.5according toFIG. 5is likewise shown as a dot-and-dash curve.

FIG. 4illustrates a double-piston compressor1.4of a compressed air supply device according to a fourth embodiment of the invention in a schematic cross-sectional view, which differs from the embodiment of the double-piston compressor1.5according toFIG. 5due to a different geometrically altered construction of the sliding block guide14.4. By way of example, in the region of the recess15″, the two sliding block tracks16″,17″ of the sliding block guide14.4are now designed to be curved in the shape of a circular arc in the direction of the piston7of the high pressure stage3.

As can be seen from the stroke curve ZH(ϕ)_1.4, shown in the graph ofFIG. 4a, of the pistons5,7or the piston rod8of the double-piston compressor1.4, this modification of the sliding block guide14.4results in the stroke width, i.e. the angle of rotation range of the piston rod8, during the stroke movement increasing in the direction of the cylinder6of the high pressure stage3, which faces the curvature of the sliding block tracks16″,17″, and the stroke width of the piston rod8during the stroke movement reducing by the same amount in the direction of the cylinder5of the low pressure stage2, which faces away from the curvature of the sliding block tracks16″,17″. In contrast, the phase position and the stroke height of the stroke curve ZH(ϕ)_1.4of the pistons5,7of the double-piston compressor1.4remain unaltered. For comparison, inFIG. 4, the stroke curve ZH(ϕ)_1.5of the pistons5,7of the double-piston compressor1.5according toFIG. 5is in turn shown as a dot-and-dash curve.

With reference to the example of the known sliding block guide14.5of the double-piston compressor1.5according toFIG. 5,FIGS. 6ato 6d, described below, show a detailed cross-sectional view of possible embodiments of the drive element12.

In the first embodiment shown inFIG. 6a, the drive element12is constructed as a crank pin13which is secured on the drive shaft10such that it is radially spaced form the axis of rotation11by the eccentricity e and is guided in a directly slideable manner on the parallel sliding block tracks16,17of the sliding block guide14.5. This embodiment of the drive element12has been used by way of example in the drawings of the embodiments of the double-piston compressor1.1-1.5inFIGS. 1 to 5. The crank pin13is clearly arranged with play in the recess15of the piston rod8.

According to the second embodiment shown inFIG. 6b, the drive element12′ is formed by the outer ring24of a rolling bearing22. The rolling bearing22is arranged with its inner ring23on a crank pin13′ which is secured on the drive shaft10such that it is radially spaced from the axis of rotation11by eccentricity e. The outer ring24of the rolling bearing22is rollably guided on the parallel sliding block tracks16,17of the sliding block guide14.5. With this embodiment of the drive element12′, the resistance and wear of the sliding block guide14.5is clearly lower than with the embodiment of the drive element12according toFIG. 6a.

In a third embodiment shown inFIG. 6c, the drive element12″ is formed by a slide bearing ring25which is slide-mounted on the outer ring24′ of a rolling bearing22′. The rolling bearing22′ is arranged with its inner ring23′ on a crank pin13′, which is secured on the drive shaft10such that it is radially spaced from the axis of rotation11by the eccentricity e. The slide bearing ring25is rollably guided on the parallel sliding block tracks16,17of the sliding block guide14.5. With this embodiment of the drive element12″, the resistance and wear of the sliding block guide14.5is again lower than with the embodiment of the drive element12′ according toFIG. 6b.

In a fourth embodiment shown inFIG. 6d, the drive element12* is formed by an externally substantially rectangular slide body27, which is rotatably mounted on a crank pin13′ via a rolling bearing26. The crank pin13′ is secured on the drive shaft10such that it is radially spaced from the axis of rotation11by the eccentricity e. The slide body27is slideably guided on the parallel sliding block tracks16,17of the sliding block guide14.5. Owing to the low surface pressure between the slide body27and the sliding block tracks16,17, the resistance and wear of the sliding block guide14.5in this embodiment of the drive element12* is also relatively low.

LIST OF REFERENCE NUMERALS