Axial piston compressor

The present invention relates to an axial piston compressor, especially a compressor for motor vehicle air-conditioning systems, in accordance with the preamble of claim 1.

In the field of compressor drive mechanisms, a trend is beginning to emerge that, in the case of compressors having variable piston stroke, increasing use is being made of tilt plates in the form of a tilt ring, that is to say ring-shaped tilt plates, with a tilt-providing articulation necessary for tilting of the plate being substantially integrated into the ring-shaped tilt plate. For example, there is known, from EP 0 964 997 B1, a compressor in which the stroke movement of the pistons is accomplished by means of engagement—in an engagement chamber—of a ring plate oriented on a slant to the machine shaft. The engagement chamber is provided adjacent to the enclosed-hollow space of the piston. For sliding engagement that is substantially free from play in any slanting position of the tilt plate or tilt ring there are provided on both sides, between it and the spherically curved inner wall of the engagement chamber, spherical segments, so-called sliding blocks, so that the tilt ring slides between them as it revolves.

The drive is transmitted from the drive shaft to the tilt ring by means of a pin for conjoint movement which is attached to the drive shaft and the spherical head of which engages in a radial bore in the tilt ring, the position of the head of the member for conjoint movement being selected so that its centre-point coincides with that of the spherical segments. In addition, that centre-point is located on a circular line which connects the geometric axes of the seven pistons with one another and, moreover, on a circular line which connects the centre-points of the spherical articulation members of the pistons. By that means, the upper dead-centre position of the pistons is determined and a minimum clearance volume is ensured. The head shape of the free end of the member for conjoint movement makes it possible for the inclination of the tilt plate to change by means of the fact that the head of the member for conjoint movement forms a bearing body for a tilting movement of the tilt plate which changes the stroke distance of the pistons.

A further precondition for tilting of the tilt plate is the displaceability of its mounting axis in the direction of the drive shaft. For the purpose, the mounting axis is formed by two mounting pins mounted on the same axis on each side of a sliding sleeve, which mounting pins are additionally mounted in radial bores in the tilt plate. For the purpose, the sliding sleeve preferably has mounting sleeves on each side, which span the annular space between the sliding sleeve and the tilt plate in the manner of spokes.

The limitation on the displaceability of the mounting axis and, as a result, the maximum angled position of the tilt plate results from the pin for conjoint movement, by virtue of the fact that the latter passes through an elongate hole provided in the sliding sleeve so that the sliding sleeve meets end stops at the ends of the elongate hole. The force for the change in the angle of the tilt plate and, therefore, for regulation of the compressor results from the sum of the pressures acting against one another in each case on each side of the pistons, so that this force is dependent on the pressure in the drive mechanism chamber. In accordance with the prior art, the pressure in the drive mechanism chamber can be regulated between a high pressure and a low pressure and consequently affects the balance of forces at the tilt plate, which influences the inclination of the latter. The position of the sliding sleeve can moreover be influenced by springs which, in various variants, are likewise included in the prior art.

Furthermore, the position of the sliding sleeve, which position governs the delivery output, is also determined by the forces of inertia acting on the tilt plate; the position of the tilt plate, that is to say its angle of tilt or slant, changes with increasing speed of rotation. In the case of modern compressors, the trend is towards using tilt plates having moments of inertia such that they bring about a reduction in the stroke distance of the pistons and therefore a reduction in delivery output when the speed of rotation increases.

However, what is problematic in the arrangement explained hereinbefore is the high Hertzian stress in the region of the head of the member for conjoint movement and the tilt plate (system: sphere/cylinder) and the take-up of the (axial) reaction forces due to the gas force on the pistons and the forces due to the torque to be transmitted to the tilt plate.

A compressor similar to the compressor known from EP 0 964 997 B1 is known from JP 2003-269330 AA, although in that compressor a total of two members for conjoint movement are used.

It is important to the kinematics according to the two mentioned publications, that is to say to the kinematics in the case of the subject-matter of EP 0 964 997 B1 and JP 2003-269330 AA, that the head of the member for conjoint movement centrally coincides with the centre-point of the sliding blocks of the pistons and that the position of the centre-point of the head of the member for conjoint movement is at the same time approximately tangential to the reference circle of the central axes of the pistons.

Added to the afore-mentioned disadvantageous characteristics is the fact that the subject-matter of EP 0 964 997 B1 and of JP 2003-269330 AA has a very complicated structural arrangement, which results in a high number of parts and therefore costs, and in addition the mounting by means of two members for conjoint movement is over-determined and therefore susceptible to wear, and the strength of the components, especially due to the fact that a hole is introduced into the shaft, has to be regarded as rather low.

A further compressor is known from DE 101 52 097 A1, differing considerably from the subject-matter of the publications discussed hereinbefore. In the case of the subject-matter according to DE 101 52 097 A1, the member for conjoint movement, in particular the spherical head of the member for conjoint movement, is replaced by a hinge pin or spindle. This is, however, integrated into the tilt plate from the outside and fastened using a cup-shaped disc for conjoint movement which is a component of the drive shaft assembly. The subject-matter of DE 101 52 097 A1 also has a complicated structural arrangement; in addition it has to be borne in mind that a large imbalance can come about, depending on the angle of tilt. This promotes wear on the compressor and as a result reduces its service life.

A further compressor is known from FR 278 21 26 A1, which has a member for conjoint movement extending out from the drive shaft radially and engaging in the tilt plate. In similar manner to the solution according to DE 101 52 097 A1, the tilt plate in this arrangement is also fixed to the member for conjoint movement in radial extension. In this there also lies a central difference from the subject-matter of EP 0 964 997 B1 and JP 2003-269330 AA. Whereas in the latter cases the mounting point of the head of the member for conjoint movement in the tilt plate undergoes relative movement in the guideway (bore) in the tilt plate because the tilt plate performs the rotary movement in an articulation lying on the shaft axis, the rotary movement in the case of the arrangements according to FR 278 21 26 A1 and DE 101 52 097 A1 is accomplished in the lateral articulation of the tilt plate.

In the unpublished Patent Application DE 102 00 404 1645 belonging to the present Applicant, there is proposed a member for conjoint movement which is displaceably mounted in the shaft. As a result, the transmission of force between the head of the member for conjoint movement and the tilt plate can be accomplished optimally (force transmission as a result of area-wise contact). However, the displacement of the member for conjoint movement in the shaft can be problematic because high forces have to be taken up there owing to the bending moment and the parts therefore have to be of very rigid construction. This rigid construction causes the compressor to have an increased mass.

Finally, from DE 103 154 77 A1 there is known a compressor of the tilt plate/member for conjoint movement constructional type wherein the member for conjoint movement does not transmit any torque. This feature in addition also applies to preferred arrangements of DE 102 00 404 1645. The conjoint movement function is restricted to providing support for the piston forces acting axially on the tilt plate, the torque being delivered by further force transmission elements independent of the member for conjoint movement. As a result, the forces acting on the member for conjoint movement are lower because, as already mentioned, no torque is transmitted. The advantage of this approach lies in the fact that the forces or contact pressure due to the forces applied (because of the fact that these forces are relatively low) do not cause any excessive deformation at and in the member for conjoint movement, as a result of which the member for conjoint movement can be of correspondingly lightweight construction and tilting of the tilt plate can be accomplished in a relatively hysteresis-free manner. However, a disadvantageous effect can be that the spherical head of the member for conjoint movement is located in a relatively large recess in the tilt plate. As a result, the Hertzian stress can or must be described by a plane/sphere geometric pairing, which is relatively disadvantageous because it causes a high degree of Hertzian stress.

Starting from the prior art explained hereinbefore, the problem of the present invention is to provide a compressor in which the head of the member for conjoint movement or its supporting element can take up forces over as great an area as possible (low Hertzian stress), whilst at the same time avoiding over-determination of force transmission functions, that is to say restriction.

The problem is solved by a compressor having the features according to patent claim 1 and 3.

A compressor according to the invention has a tilt plate, especially a ring-shaped tilt plate, which is variable in terms of its inclination to a drive shaft and which is driven in rotation by the drive shaft and is in articulated connection with at least one supporting element arranged at a spacing from the drive shaft and rotating together therewith. The pistons of the axial piston compressor in each case have an articulated arrangement with which the tilt plate is in sliding engagement. The supporting element is arranged at the radially outer end of a force transmission element which rotates together with the drive shaft and which is fixed in the latter so as to be non-displaceable in the radial direction, a fundamental point of the invention being that the force transmission element is mounted in the drive shaft so that it can rotate about its longitudinal axis. By this means it is ensured that no undesirable moments, especially torsional moments, act on the force transmission element and also on the supporting element and result in increased wear.

In a preferred embodiment of a compressor according to the invention, the supporting element and force transmission element serve substantially only for providing axial support for the pistons or support for the gas force, whereas the torque transmission between the drive shaft and tilt ring is accomplished by a specific arrangement independent of the supporting element and force transmission element. This arrangement is especially an articulated connection between the drive shaft and the tilt plate. As a result of separation of the arrangement serving for providing axial support for the pistons or support for the gas force from an arrangement dedicated to driving the tilt plate or tilt ring, the arrangement serving for providing support for the gas force can firstly be slimmer and therefore of lighter construction, and furthermore there is obtained the advantage that the moments acting on the supporting element and the force transmission element can be reduced, which, as already mentioned hereinbefore, ensures less wear on the compressor according to the invention.

A further solution to the problem of the present invention is obtained when the supporting element in a compressor according to the preamble of patent claim 1 has a basic shape which in radial section is approximately rectangular, the “corners” being highly rounded especially with different radii, or also alternatively in the form of a compressed or deformed circle or also of an ellipse, which can in turn be deformed or compressed. As a result, the contact pressure or deformation in the region of the supporting element and tilt plate is advantageously influenced. Of course, a combination of the features of patent claims 1 and 3 is also possible

Those regions of the supporting element which are in contact with the tilt plate or tilt ring can be of at least partly cylindrical or barrel-shaped construction. As a result of a cylindrical or barrel-shaped contour, the tilt plate is approximately in line contact with the supporting element. It should be pointed out that the contour of the supporting element as described above can be machined to shape or ground by means of a shaping tool, which ensures simple and, as a result, economical manufacture.

In the case of a coolant compressor of the described mode of construction or in the case of a coolant compressor according to the preamble of patent claim 1, it is possible to differentiate between two moments in respect of the tilting of the tilt plate. These moments are, on the one hand, a tilting moment (in the tilting plane) and, on the other hand, a torsional moment, which acts perpendicular to the afore-mentioned tilting moment. The torsional moment arises inter alia because the maximum gas force at a piston arises at the moment of opening of the valve and not at the upper dead-centre of the piston. The resulting reaction force of all the pistons directs itself to a large extent to that piston which is in the state described. In a preferred embodiment, support for the torsional moment is provided in the region of the drive shaft, which is accomplished especially by means of an arrangement which is provided between a sliding sleeve mounted on the drive shaft in displaceable manner and the tilt plate. An arrangement of such a kind can consist of one or more cylindrical-pin-like element(s) or of supporting or contact surfaces. At this juncture it should be pointed out that the tilt plate is pivotally mounted on the afore-mentioned sliding sleeve, which is mounted so as to be axially displaceable along the drive shaft. As a result, as already mentioned hereinbefore, support is provided for a torsional moment acting in the region of the drive shaft. The force transmission element can furthermore have, at least over parts of its periphery, a shoulder in the region of the drive shaft and, additionally or alternatively, can comprise at its end remote from the supporting element a securing element, especially extending in the axial direction. The shoulder in the region of the drive shaft ensures that the force transmission element has a defined position in the drive shaft in a simple structural arrangement, and a securing element ensures secure holding in the drive shaft. The tilt plate is connected to the sliding sleeve and to the drive shaft preferably by means of drive pins, especially in a constructional form in which the force transmission element and the supporting element serve solely as support for the gas force. This ensures a reliable, structurally simple drive to the tilt plate, whereas at the same time the advantages of separating the drive from the provision of support against gas forces come into effect. For a secure hold, the drive pins can be introduced into the sliding sleeve or the tilt plate with a press fit. Furthermore, the drive pins can project into a recess, especially a groove, in the drive shaft, in which case furthermore a connecting element, especially a feather key, can be arranged between the drive shaft and the sliding sleeve, which connecting element allows transmission of forces and moments in a radial direction and is mounted in axially displaceable manner on the drive shaft. This ensures a relatively simple variant of the axial piston compressor according to the invention which can be produced using just a few individual parts.

A further preferred structurally simple embodiment of a compressor according to the invention is obtained when that end of the force transmission element which is remote from the supporting element projects through the drive shaft and into a longitudinal slot in the sliding sleeve in such a way that drive torque is transmitted from the drive shaft to the sliding sleeve by means of that end of the force transmission element which is remote from the supporting element.

In a particular embodiment, the supporting element is so constructed that it is located within a recess in the tilt plate in line contact with the latter, which ensures optimum Hertzian stress and also optimum force transmission. The height of the recess in the tilt plate can be equal to the sum of the radii of curvature of a radially outer and a radially inner contour, which ensures an ideal curve profile for the gas force support means. On that side of the tilt plate which is subject to greater loading by the gas force, the wall thickness in the region of the recess in the tilt plate is preferably greater than on that side which is subject to less loading, whilst furthermore at the same time the clearance volume is constant for all tilt angles of the tilt plate. Normally, that side of the tilt plate which is subject to greater loading by the gas force is the side facing the pistons. This structural measure increases the stability of the tilt plate, whilst at the same time the thinner wall thickness on that side which is subject to less loading makes it possible to save weight.