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Axial piston compressor

Axial piston compressor description/claims

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

From DE 197 49 727 A1 there is known an example of an axial piston compressor of such a kind, having a housing and, arranged in the housing and driven by way of a drive shaft, a compressor unit for drawing in and compressing a coolant. The compressor unit is regulated substantially by the pressure PC in a drive mechanism chamber depending in the particular instance on the load and/or speed of rotation of the compressor, an inlet pressure PV1 and a high pressure PV2 that prevail on the inlet and outlet sides, respectively, of the compressor also having an influence on regulation of the compressor. Regulation takes place by way of a change in the piston stroke of the compressor, the piston stroke being governed by the deflection of a tilt plate from a zero position.

In the case of such an axial piston compressor it is additionally the case, however, that because of the force conditions prevailing in the compressor, especially because of centrifugal forces, the compressor has a tendency to up-regulate at high speeds of rotation, that is to say the compressor has a tendency towards a greater piston stroke and accordingly towards a higher pressure on the high-pressure side.

DE 195 14 748 C2 explains the tilting moments which in the case of, in principle, all compressors existing in the prior art of the tilt plate form of construction act on the tilt plate and which decisively contribute to the tilting or, that is to say, inclination behaviour of the tilt plate. The compressor tilting behaviour described in that publication can be regarded as being exemplary of compressors of the tilt plate form of construction. In general it is the moments given below which, in the centre of the tilting movement of the tilt plate, have an influence on the tilting of the tilt plate. The direction of the moment is given in brackets, with (−) denoting down-regulation, that is to say regulation in the direction of minimum stroke, and (+) denoting up-regulation, that is to say regulation in the direction of maximum stroke of the pistons. It is substantially the following moments that play a part: moment due to gas forces in the cylinder spaces (+) moment due to gas forces from the drive mechanism chamber (−) moment due to a restoring spring (−) or moment due to an advancing spring (+) moment due to rotating masses (−), these including, for example, the tilt plate (including a moment due to the position of the centre of gravity, in which case—for example in accordance with DE 195 14 748 C2—this component can be positive, that is to say (+)) moment due to masses moved in translation (+), which can include, for example, pistons, sliding blocks or also an oscillating wobble plate.

As can be seen from the above listing, the moment due to the rotating masses, hereinafter referred to as MSW, generally has a down-regulating action over an extensive tilt angle range. It is only in the region of very small tilt angles, as a result of, for example, an outwardly displaced location of centre of gravity (Steiner component in the calculation of the moment of deviation Jyz) that an up-regulating moment can be produced in the case of the tilt plate. DE 195 14 748 C2 also shows a plot of the moment due to masses moved in translation, which as already explained has an up-regulating action.

Also of interest is the sum of the moments, which in the case of the subject-matter of DE 195 14 748 C2 is responsible for up-regulating behaviour of the compressor over the entire tilt angle range of the tilt plate, because the masses moved in translation dominate the regulation behaviour in a wide tilt angle range.

With reference to the prior art, especially according to DE 195 14 748 C2, it is disadvantageous therein that, when there is an increase in the delivery volume due to an increase in the speed of rotation, an additional increase in the delivery volume due to an increase in the tilt angle of the tilt plate is added thereto. This has to be compensated by appropriate interventions for the purpose of regulation, which is onerous, reduces the efficiency of the driving engine and accordingly increases the fuel consumption.

From EP 0 809 027 A1 there is known a compressor in which an attempt is made so to compensate the delivery quantity of the compressor by means of the dynamic behaviour of the compressor drive mechanism that the delivered quantity of coolant or, that is to say, the coolant mass flow can be kept constant. For regulating the delivery quantity so that it is constant in the case of changing speeds of rotation it is proposed that the restoring torque of the wobble plate be utilised, the inclined position of which is counteracted by the restoring torque by virtue of dynamic forces on the co-rotating plate part.

Measures are known from DE 198 39 914 A1 as to how regulation behaviour of such a kind—that is to say, at least partial compensation of the delivery quantity—can be achieved. It is proposed that the tilt plate component mass be so dimensioned in relation to the masses moved in translation that the centrifugal forces of the tilt plate influence the regulation behaviour of the tilt plate. According to DE 198 39 914 A1 it is proposed that the rotating mass of the tilt plate or, that is to say, of the tiltable part of the tilt plate be greater than the total mass of all the pistons so that the centrifugal forces occurring during rotation of the tilt plate are sufficient to counteract the tilting movement of the tilt plate in regulating manner deliberately and thereby to influence, especially to reduce or to limit, the piston stroke and, accordingly, the delivery quantity.

In DE 103 29 393 A1 belonging to the Applicant it is furthermore explained why the component mass should not be the preferred parameter for influencing as desired the regulation behaviour of the drive mechanism resulting from changes in the speed of rotation. According to DE 103 29 393 A1, the desired regulation behaviour of the compressor is primarily achieved not by means of the tilt plate component mass in relation to the masses moved in translation but rather by taking into account the mass moment of inertia of the tilt plate arrangement, which depends more on its geometry than on its component mass. A central concept in that Application is that, in the case of fluctuations or changes in the speed of rotation, the moment due to masses moved in translation is directly compensated, or even over-compensated, by the moment due to rotating masses. In the case of new compressors it is in fact desirable to reduce to a low level the frequency and intensity of interventions for the purpose of regulation.

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