EP1218639A1

EP1218639A1 - Axial piston displacement compressor

Info

Publication number: EP1218639A1
Application number: EP00969409A
Authority: EP
Inventors: Otfried Schwarzkopf
Original assignee: Zexel Valeo Compressor Europe GmbH
Current assignee: Valeo Compressor Europe GmbH
Priority date: 1999-10-04
Filing date: 2000-10-04
Publication date: 2002-07-03
Anticipated expiration: 2020-10-04
Also published as: WO2001025635A1; DE19947677A1; AU7913700A; US6766726B1; EP1218639B1; DE19947677B4; DE50010473D1

Abstract

The invention relates to an axial piston displacement compressor, comprising a drive shaft (12), a disc (14) which is mounted on the drive shaft in such a way, that it can be pivoted about a pivotal axis (C) and at least one piston (18) which is provided with sliding blocks (20) that slide on a runway on the disc (14). The invention aims to reduce the maximum effective surface pressure between the disc (14) and the sliding blocks (20). To this end, the pivotal axis (C) of the disc (14) is located eccentrically in relation to the central plane of the disc.

Description

axial piston

State of the art

The invention relates to an axial piston compressor with a drive shaft, a disc which is mounted on the drive shaft so that it can be displaced relative to it about a pivot axis, and at least one piston which is provided with sliding blocks which run on a track on the disc slide.

Such an axial piston compressor can be used in particular in an air conditioning system for motor vehicles. It serves to draw off a refrigerant from a heat exchanger, in which it evaporates while absorbing heat, and to compress it to a higher pressure, so that it can emit the heat again at a higher temperature level in a further heat exchanger. The refrigerant is then throttled to the pressure level of the first heat exchanger in an expansion device.

Refrigerant compressors of various types are used for applications in vehicle air conditioning systems. In recent years, axial piston compressors have prevailed for a number of reasons, in particular since this type of construction makes it possible to implement an energetically favorable power control. Since the compressor is usually coupled directly to the motor via a belt drive, the speed of the compressor cannot be adjusted in view of the desired operating conditions of the compressor; for this reason, the output is adjusted by pivoting the disc, which determines the stroke volume of the pistons of the compressor. The stroke of each piston is caused by the interaction of the sliding blocks connected to the piston with the disk, which can be pivoted relative to the drive shaft. If the disc is not pivoted relative to the drive shaft, i.e. the center axis of the disc coincides with the longitudinal axis of the drive shaft, there is no stroke, since the distance between, for example, the bottom of the cylinder in which the piston is arranged and the tread is at Revolution of the drive shaft does not change. On the other hand, if the disc is pivoted so that the central axis of the disc includes an angle other than zero with the longitudinal axis of the drive shaft, which is usually a maximum of 20 °, the distance between the tread of the disc and the bottom of the cylinder changes with each revolution of the Drive shaft periodically between a minimum value and a maximum value. The piston coupled to the disk is thus, when the distance is minimal, at its top dead center, that is to say pushed into the cylinder to the maximum, while it is at its maximum dead center in its bottom dead center.

The track of the sliding parts attached to the pistons on the disc changes depending on the pivoting angle of the disc.

If the central axis of the disc coincides with the longitudinal axis of the drive shaft, the sliding blocks on the disc have a circular track. The radius of this raceway corresponds to the distance between the center of the sliding blocks and the longitudinal axis of the drive shaft. If, on the other hand, the disc is pivoted, the sliding blocks on the disc have an elliptical track, since the distance between the center of the sliding blocks and the longitudinal axis of the drive shaft remains unchanged. The short semiaxis of the ellipse has a length that corresponds to the radius of the circular raceway when the disk is not pivoted, and is parallel to the pivot axis of the disk. The length of the long semi-axis of the ellipse results from the radius divided by the cosine of the swivel angle of the disc. In order to obtain a compact compressor, the pivotable disk is dimensioned such that when the disk is not pivoted, only a very small edge remains between the track of the sliding blocks and the outer rim of the disk. It follows from this that when the disk is pivoted, the track of the sliding blocks in the areas of the disk which correspond to the top and bottom dead center of the pistons extends beyond the edge of the disk. This is a consequence of the apparent shortening of the disc when it is pivoted. The fact that the track extends beyond the edge of the disk in the pivoted state results in a reduced area which is available for transmitting the forces between the disk and the sliding blocks. In addition, in one of the positions in which the sliding blocks protrude beyond the outer edge of the disk, namely the position corresponding to the top dead center of the piston at the end of the compression stroke, the maximum force acts between the sliding blocks and the disk. The coincidence of the reduction in the area available for power transmission on the one hand with the maximum of the force to be transmitted on the other hand leads to an increase in the surface pressure between the disk and the raceway, which in extreme cases can lead to seizure between the sliding block and the disk.

The object of the invention is therefore to improve an axial piston compressor of the type mentioned in such a way that seizure between the sliding blocks and the disk is reliably prevented under all operating conditions.

Advantages of the invention

In an axial piston compressor according to the invention with the features of the characterizing part of claim 1, due to the offset between the central plane of the disc and the pivot axis of the disc, a translatory movement is superimposed on the rotary movement of the disc. This leads to the fact that the disc is relative to the sliding blocks, their position is specified, moves when pivoting. This shift can be used in a targeted manner to either completely eliminate or significantly reduce the emergence of the sliding block raceway over the edge of the disk. This eliminates or reduces the increase in surface pressure between the sliding block and the raceway.

It is preferably provided that the pivot axis of the disk lies on the side facing the piston with respect to the central plane of the disk. With this design, the reduction in the overlap between the sliding blocks and the disc is counteracted by the pivoting of the disc in the region which corresponds to the top dead center of the respective piston, that is to say at the operating point in which the force acting on the piston is greatest. The resulting reduction in the overlap between the sliding block and the raceway of the disk, which is twice as large as in a design according to the prior art with a pivot axis which coincides with the central plane of the disk, can be tolerated, since the corresponding Force on the piston at the time is comparatively low. The surface pressure that results despite the reduction in the contact area between the sliding blocks and the track of the disk is below the critical values.

According to a preferred embodiment of the invention, the disc is a swash plate, which can be set in rotation by the drive shaft and whose swivel angle can be adjusted with respect to the drive shaft. Such an axial piston compressor, which, apart from the translational movement which is superimposed on the rotational movement of the disk, corresponds to a design known for example from DE 197 03 216 A1, combines the advantage achieved according to the invention of reducing the surface pressure at certain points in time during operation, for example the point in time maximum force acting on the piston, with this design's own advantage of a comparatively simple structure. According to an alternative preferred embodiment, it is provided that the disc is a swash plate which is rotatably mounted on a swash plate and whose swivel angle with respect to the drive shaft corresponds to that of the swash plate. This type of construction, which apart from the translatory movement of the swash plate, which is superimposed on the rotary movement when swiveling, corresponds to a type of construction as is known, for example, from DE 196 21 174 A1, combines the advantage of a targeted reduction in surface pressure with that of this type own advantage of a particularly low-friction operation.

According to a preferred embodiment of an axial piston compressor according to the invention it is provided that at a distance between the longitudinal axis of the drive shaft and the longitudinal axis of the piston of 30 mm, a diameter of the flat surface of the sliding blocks bearing against the raceway of 8 mm and a maximum swivel angle between the longitudinal axis of the drive shaft and the center axis of the disc of 18 °, the distance between the center plane of the disc and the pivot axis of the disc is about 1 mm. With this slight offset between the pivot axis and the center plane of the disc, the disc is only displaced so far when pivoting relative to the track of the sliding blocks that there is a reduction in the protrusion of the track over the outer edge of the disc on one side of the disc; The theoretically possible displacement of the disc to such an extent that the raceway is again completely on the disc in the area of a dead center of the piston is deliberately not sought, since with increasing offset between the pivot axis and the center plane of the disc, the center of gravity of the disc against the Longitudinal axis of the drive shaft migrates. Given the geometric conditions mentioned, the value given represents a good compromise between a reduction in the surface pressure on the one hand and an increase in the imbalance of the disk on the other. Advantageous refinements of the invention result from the subclaims.

drawings

The invention is described below with reference to the accompanying drawings. In these show:

- Figure 1 is a schematic sectional view of an axial piston compressor according to the prior art;

- Figure 2 on an enlarged scale, the detail II of Figure 1;

- Figure 3 is a diagram of the force acting on the piston as a function of the angle of rotation;

- Figure 4 schematically shows the geometry between the disc and sliding blocks in an axial piston compressor according to the prior art;

- Figure 5 schematically shows a further representation of the geometric relationships in an axial piston compressor according to the prior art; and

- Figure 6 shows a schematic representation of the geometric relationships in an axial piston compressor according to the invention.

Description of the embodiment

1 shows an axial piston compressor according to the prior art. This contains a housing 10 in which a drive shaft 12 is rotatably mounted. A swash plate 14 is connected in a rotationally fixed manner to the drive shaft 12 and is attached pivotably about a pivot axis C. The pivot axis C intersects the longitudinal axis L of the drive shaft 12 on the right Angle. The swash plate 14 can be swiveled about the swivel axis C between a position in which the swivel angle between the center plane M of the swash plate 14 and a plane perpendicular to the longitudinal axis L of the drive shaft is approximately zero, and a maximally swiveled position in which the swivel angle α is approximately Is 20 °. The manner in which the adjustment of the swash plate 14 is achieved and controlled is, on the one hand, generally known and, on the other hand, not relevant for the understanding of the invention, so that this is not dealt with.

A plurality of cylinders 16 are formed in the housing, in each of which a piston 18 is slidably mounted. The longitudinal axis Z of each piston and each cylinder is aligned parallel to the longitudinal axis L of the drive shaft. The compressor can be provided with up to seven such pistons, which are arranged at a uniform angular distance around the drive shaft.

Each piston is provided with two sliding blocks 20, each of which has a circular plane surface 22 and a spherical segment-shaped swivel surface 24. The pivot surface of each slide block 20 is received in a correspondingly shaped receiving surface 26 on the piston so that the swash plate 14 is received between the mutually facing and parallel plane surfaces 22 of the two slide blocks of a piston. In this way, when the swash plate 14 is swiveled by a swivel angle α other than zero, the wobbling rotational movement of the swash plate is converted into a translatory movement of the pistons 18. The flat surfaces 22 of the sliding blocks 20 run on raceways on the swash plate 14, which change with the swivel angle α. If the central axis of the swash plate 14 coincides with the longitudinal axis L of the drive shaft 12, that is to say the swash plate 14 extends perpendicular to the drive shaft 12, there is a circular raceway of the sliding blocks 20 on the swashplate 14. The radius of this raceway corresponds to the distance between the center point of the of the receiving surfaces 26 defined ball joint of each cylinder and the longitudinal axis L. Since in the embodiment shown the center of each Ball joint lies on the longitudinal axis Z of each cylinder 16, the radius of the raceway corresponds to the distance between the longitudinal axis Z and the longitudinal axis L If, on the other hand, the swivel plate is pivoted out of its orientation perpendicular to the drive shaft 12, an elliptical raceway results. This is due to the fact that in the two dead centers of the pistons, which are shown in FIG. 1, each plane surface is at a greater distance from the pivot point C of the swash plate 14 than in the intermediate positions offset by 90 °.

Since, for reasons of space, the outer diameter A of the swash plate 14 is selected such that the swash plate slightly protrudes beyond the radially outer side of the sliding blocks 20 in the non-pivoted state, the track of the sliding blocks 20 lies on the value A due to the apparent shortening of the outer diameter of the swash plate 14 'no longer completely on the swashplate; the flat surface 22 of the sliding blocks is therefore no longer completely on the swash plate 14. The extent to which the flat surface 22 projects beyond the outer rim of the swash plate 14 is denoted by a in the figures. A snapshot with the swash plate 14 pivoted by the swivel angle α is shown in FIG. 4 for the time when the pistons pass through the top and bottom dead centers. FIG. 5 shows a projection of a sliding block 20 and the swash plate 14 into a plane perpendicular to the longitudinal axis L of the drive shaft 12 for the moment of passage through a dead center of the piston. It can clearly be seen that the sliding block 20 projects beyond the outer circumference of the disk 14 by the projection a. With a distance between the longitudinal axis Z of the piston and the longitudinal axis L of the drive shaft 12 of 30 mm, a diameter of the plane surface 22 of the sliding blocks 20 of 8 mm and a maximum swivel angle of 18 °, it results from the geometric conditions that the projection a = 1.6 mm. This results in an area U = 7.2 mm ² protruding beyond the swash plate 14, while the remaining area lying on the swash plate 14 is R = 43 mm ² . Since almost 14.5% of the flat surface 22 of the sliding blocks 20 are thus not available for power transmission, this increases accordingly the surface pressure in the area of the remaining surface R. On the one hand, in addition to this, the planar surfaces 22 are inclined relative to the longitudinal axis Z of each cylinder at each of the dead centers, so that for the actually prevailing surface pressure only the surface of the surface projected into a plane perpendicular to the longitudinal axis Z. Planned space is available. On the other hand, the maximum force between the swash plate and the corresponding piston acts at the top dead center of each piston. The diagram shown in FIG. 3 shows the course of the force F acting on the piston as a function of the angle of rotation φ of the swash plate 14. The angle of rotation φ = 0 ° corresponds to the top dead center of a piston, that is to say the maximum state pushed into the cylinder 16. Starting from top dead center, the piston is first accelerated towards bottom dead center, while at the same time refrigerant is drawn in. For this reason, the forces acting on the piston are negative in some areas. After reaching the bottom dead center, which corresponds to a rotation angle of φ = 180 °, the compression stroke follows, in which the piston is accelerated towards top dead center, while the refrigerant is compressed at the same time. The forces acting on the piston increase, the maximum forces acting shortly before top dead center is reached.

From this course of the force acting on the piston, in conjunction with the geometric conditions, it follows that the smallest part of the plane surfaces 22 is available for the power transmission on the one hand in the area of the bottom dead center, that is in the area of the transition from the intake stroke to the compression stroke. However, the increase in surface pressure resulting from the projection of the plane surfaces 22 over the outer edge of the swash plate 14 is not critical, since comparatively small forces have to be transmitted in this area. On the other hand, there is the same protrusion of the flat surfaces of the sliding blocks over the outer edge of the swash plate 14 in the area of the top dead center. However, since the highest forces have to be transmitted between the swash plate 14 and the sliding blocks 20 here, there is a critical increase in the surface pressure between the corresponding ones Flat surface 22 and the swash plate 14. This surface pressure can assume such values that seizure can occur between the swash plate 14 and the flat surface 22 of the sliding block 20.

The described increase in surface pressure between the sliding blocks 20 and the swash plate 14 in the area of the top dead center of the corresponding piston can be reduced or eliminated by the configuration according to the invention. The configuration according to the invention is shown schematically in FIG. In contrast to the design known from the prior art, the pivot axis C is offset here by a dimension V with respect to the central plane of the swash plate 14. The offset V is chosen so that the pivot axis C lies on the side of the pistons (not shown in FIG. 6) which are driven by the swash plate 14. Due to the offset V, when the swash plate 14 is pivoted, a translatory movement occurs in addition to the rotary movement. As a result, the outer edge of the swash plate 14, viewed for the positions corresponding to the dead centers of the pistons, is arranged eccentrically. In this way it is achieved that the track 20 of the sliding blocks in the area of the top dead center of the corresponding piston is again completely on the swash plate 14; the supernatant a is zero. Thus, the full surface of the flat surface 22 is again available for power transmission. In return, the protrusion of the sliding block has doubled in the area of the raceway that corresponds to the lower pressure point of the piston; the resulting increase in surface pressure is not critical, however, since only small forces have to be transmitted in the area of the lower pressure point of the piston.

In Figure 6, the offset V of the pivot axis C relative to the center plane of the swash plate 14 is shown exaggerated; in practice, an offset V of the order of magnitude of 2 mm is sufficient for the size ratios given above to eliminate the projection A for the top dead center of the piston. Due to the reduction in the surface pressure between the sliding blocks and the swash plate at maximum load, the sliding block can possibly be made with smaller dimensions. This enables a more compact design. Since the flat surface 22 of the sliding blocks 20 no longer runs over the edge of the swash plate 14 at maximum load, stress peaks and thus the wear caused by edge pressure are reduced. Due to the increased projection a of the flat surface 22 in the area of bottom dead center, there is an improved wetting of the flat surface of the sliding parts by the oil mist inside the housing 10.

When the swivel axis C is arranged eccentrically with respect to the center plane of the swash plate, when the swash plate 14 is pivoted, the center of gravity of the swash plate is arranged eccentrically with respect to the longitudinal axis L of the drive shaft. This tends to result in low imbalances when operating the compressor. Since these unbalances increase with increasing offset V, a compromise can be made not to compensate for the entire projection a in the area of the top dead center, but only to such an extent that the surface pressure only rises to an acceptable level. For example, with the above-described geometrical dimensions with an offset V of 1 mm, the surface pressure in the area of the top dead center can be reduced by around 10% compared to the prior art, while at the same time the center of gravity of the swash plate 14 only by 0.3 mm the longitudinal axis L of the drive shaft migrates.

The principle described according to the invention, i.e. the pivoting of a disc about a pivot axis, which is arranged eccentrically with respect to the central plane of this disc, can of course also be applied to those axial piston compressors in which the sliding blocks of the pistons do not act directly on the swash plate itself, but on one Swashplate rotatably mounted on the swashplate. LIST OF REFERENCE NUMBERS

10: housing

12: drive shaft 14: swash plate

16: cylinder

18: Piston

20: sliding block

22: flat surface 24: swivel surface

26: receiving surface

A: Outside diameter swash plate

A ': Apparent outside diameter of the swash plate

C: swivel axis L: longitudinal axis of the drive shaft

R: remaining area

Ü: protruding surface

V: offset

Z: longitudinal axis of piston and cylinder α: swivel angle φ: angle of rotation of the swash plate

Claims

claims

1. axial piston compressor with a drive shaft (12) of a disc (14) which is mounted on the drive shaft so that it can be pivoted relative to the drive shaft about a pivot axis (C), and at least one piston (18) with at least two Sliding blocks (20) are provided which slide on a track on the disc (14), the piston (18) encompassing the sliding blocks (20) in a C-shape, characterized in that the pivot axis (C) of the disc (14) is eccentric is arranged with respect to the central plane of the disc in order to move the disc (14) relative to the sliding blocks (20) such that the track of the sliding blocks does not extend or only extends slightly beyond the edge of the disc.

2. Axial piston compressor according to claim 1, characterized in that the pivot axis (C) of the disc lies with respect to the central plane of the disc on the side facing the piston (18).

3. Axial piston compressor according to one of the preceding claims, characterized in that the disc is a swash plate (14) which can be set in rotation by the drive shaft (12) and whose swivel angle (α) can be adjusted with respect to the drive shaft.

4. Axial piston compressor according to one of claims 1 and 2, characterized in that the disc is a swash plate which is rotatably mounted on a swash plate and whose angle of rotation with respect to the drive shaft corresponds to that of the swash plate.

5. Axial piston compressor according to one of the preceding claims, characterized in that at a distance between the longitudinal axis (L) Drive shaft and the longitudinal axis (Z) of the piston of 30 mm, a diameter of the contact surface (22) of the sliding blocks (20) of 8 mm and a maximum swivel angle (α) between the longitudinal axis of the drive shaft and the central axis of the disc of 18 ° the distance between the center plane of the disc and the pivot axis of the disc (14) is not greater than about 1 mm.