Device for damping pressure pulsations for a compressor of a gaseous fluid

Abstract

The invention relates to a device (1) for damping pressure pulsations for a compressor of a gaseous fluid, in particular of a refrigerant. The device comprises a housing (2), a piston element (6) as well as a spring element (8). The housing (2) is developed encompassing a chamber (3), with an inlet opening (4) and an outlet opening (5). The piston element (6), supported such that it is stayed across the spring element (8) on the housing (2), is disposed within the chamber (3) dividing the chamber (3) into a first chamber volume (3a) and a second chamber volume (3b), as well as being disposed movably in a direction of motion (11) between a first end position and a second end position. The motion of the piston element (6) effects a change of the chamber volumes (3a, 3b) and of a flow cross section of the outlet opening (5). The piston element (6) is developed as a hollow cylinder with two, at least partially closed, end faces (7, 13). The piston element (6) herein comprises at least one through-opening (14, 15) developed as a fluidic connection between a chamber volume (3a, 3b) and a volume encompassed by a wall of the piston element (6).

Claims

1. A device for damping pressure pulsations for a compressor of a gaseous fluid comprising: a housing that encompasses a chamber and is implemented with an inlet opening and an outlet opening, a piston element which within the chamber divides the chamber into a first chamber volume and a second chamber volume, as well as being disposed movably in a direction of motion between a first end position and a second end position, wherein the motion of the piston element controls the size of both chamber volumes and a flow cross section of the outlet opening, as well as being supported stayed on the housing across a spring element, wherein the piston element includes: a side wall closing a lateral area of the piston element over the entire surface of the side wall, a first end wall partially closing one end of the piston element, a second end wall at least partially closing the other end of the piston element, and a volume encompassed by the side wall, the first end wall and the second end wall, wherein the first end wall includes a first through opening formed as a fluidic connection between the first chamber volume and the volume of the piston element, and wherein the second end wall includes a second through opening formed as a fluidic connection between the second chamber volume and the volume of the piston element; wherein the gaseous fluid is a refrigerant.

2. The device according to claim 1, wherein the piston element is formed as a circular cylinder.

3. The device according to claim 2, wherein the volume of the piston element is an inner volume, and the piston element has a transmission loss according to the formula: $D_{\mathrm{TL}}=10\log \left(\frac{{\left({}_A+{}_E\right)}^2{\cos }^2\left(\mathrm{kL}\right)+{\left(1+{}_A{}_E\right)}^2{\sin }^2\left(\mathrm{kL}\right)}{4{}_A{}_E}\right)$ $\mathrm{with}{}_A=\frac{S}{S_A}\mathrm{and}{}_E=\frac{S}{S_E}\mathrm{and}k=\frac{w}{c}=\frac{2}{}.$ wherein D.sub.TL is the transmission loss of the piston element, L is a length of the inner volume of the piston element, S is a cross sectional area of the inner volume of piston element, S.sub.E is a cross sectional area of the first through-opening for inflow of the refrigerant into the piston element and S.sub.A is a cross sectional area of the second through-opening for outflow of the refrigerant from the piston element.

4. The device according to claim 1, wherein the inlet opening is developed in a wall of the chamber at a first end face.

5. The device according to claim 1, wherein the piston element is formed as a circular-shaped piston element and the direction of motion is oriented along a longitudinal axis of the cylinder-shaped piston element.

6. The device according to claim 1, wherein a first end face of the piston element is disposed such that it is oriented toward the inlet opening.

7. The device according to claim 1, wherein the spring element is developed as a helical spring.

8. The device as in claim 7, wherein the spring element is disposed with a longitudinal axis on a longitudinal axis of the piston element.

9. The device as in claim 7, wherein a first end of the spring element is disposed such that it is in contact with a wall closing off the chamber at a second end face.

10. The device according to claim 7, wherein a second end, developed distally to a first end of the spring element, is oriented in the direction toward the inlet opening and is disposed such that it is in contact with an outer side of the piston element.

11. The device as in claim 10, wherein the second end of the spring element is disposed such that it is in contact with the second end wall of the piston element.

12. The device according to claim 1, wherein the piston element in the first end position is disposed at a minimal distance from the inlet opening such that the flow cross section of the outlet opening is closed and the size of the first chamber volume has a minimal value and the size of the second chamber volume has a maximal value.

13. The device according to claim 1, wherein the piston element in the second end position is disposed at a maximal distance from the inlet opening such that the flow cross section of the outlet opening is completely opened and the size of the first chamber volume has a maximal value and the size of the second chamber volume has a minimal value.

14. The device according to claim 1, wherein the outlet opening is connected with a suction region of the compressor.

15. A method for cooling a motor vehicle with a refrigerant compressor having a device for damping pressure pulsations of a refrigerant, the device comprising: a housing that encompasses a chamber and is implemented with an inlet opening and an outlet opening, a piston element which within the chamber divides the chamber into a first chamber volume and a second chamber volume, as well as being disposed movably in a direction of motion between a first end position and a second end position, wherein the motion of the piston element controls the size of both chamber volumes and a flow cross section of the outlet opening, as well as being supported stayed on the housing across a spring element, wherein the piston element includes: a side wall closing a lateral area of the piston element over the entire surface of the side wall, a first end wall partially closing one end of the piston element, a second end wall partially closing the other end of the piston element, and a volume encompassed by the side wall, the first end wall and the second end wall, wherein the first end wall includes a first through opening formed as a fluidic connection between the first chamber volume and the volume of the piston element, and wherein the second end wall includes a second through opening formed as a fluidic connection between the second chamber volume and the volume of the piston element, the method comprising the step of operating the refrigerant compressor having the device to cool the motor vehicle.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1A: a prior art device for damping pressure pulsations for a compressor within a chamber encompassed by a housing in sectional representation in the closed state, as well as

(2) FIG. 1B: according to FIG. 1A in an opened state,

(3) FIG. 2A: a device according to the invention for damping pressure pulsations for a compressor within the chamber encompassed by the housing in sectional representation in a first end position,

(4) FIG. 2B: according to FIG. 2A in an intermediate position as well as

(5) FIG. 2C: according to FIG. 2A in a second end position,

(6) FIG. 3A: a piston element of a device according to the invention for damping pressure pulsations for a compressor in sectional representation, and

(7) FIG. 3B: transmission losses depending on the frequency based on simulation calculations and measurements for a specific device according to the invention.

DETAILED DESCRIPTION

(8) In FIGS. 1A and 1B is shown a device 1 of prior art for damping pressure pulsations for a compressor within a chamber 3 encompassed by a housing 2 in sectional representation. In FIG. 1A the device 1 is shown in a closed state, while the device 1 according to FIG. 1B is shown in an opened state.

(9) The housing 2 encompassing the chamber 3 comprises an inlet opening 4 as well as an outlet opening 5, each of which being implemented in the wall of the housing 2. The fluid to be compressed during its flow through the compressor flows through the inlet opening 4 into the chamber 3 and out of the chamber 3 through the outlet opening 5. The inlet opening 4 is developed as a connection to a low-pressure side of a refrigerant circulation, while the outlet opening 5 is connected with a suction region of the compressor. The inlet opening 4 is implemented in a wall closing off the chamber 3 at a first end face, while the outlet opening 5 is implemented on a wall closing off the chamber 3 at a lateral face.

(10) Within the chamber 3 a piston element 6 is disposed such that it is movable within the chamber 3 in a direction of motion 11. The direction of motion 11 is herein oriented along a longitudinal axis of the cylinder-shaped piston element 6. With its motion in the direction of motion 11 the piston element 6 controls an open flow cross section of the outlet opening 5, The flow cross section of outlet opening 5 is maximally opened when the piston element 6 in the direction of motion 11 has a maximal distance from the inlet opening 4. The flow cross section of the outlet opening 5 is closed when the piston element 6 in the direction of motion 11 is disposed at a minimal distance from the inlet opening 4. The wall of housing 2 corresponds to the outer form and the outer dimensions of the piston element 6.

(11) The piston element 6 is supported such that it is stayed on the housing 2 across a spring element 8. The spring element 8 can herein be implemented as a helical spring, in particular as a compression spring, or be implemented of plate springs. A first end 9 of the helical spring-shaped spring element 8 is disposed in contact on a wall closing off the chamber 3 at a second end face. A second end 10, distal with respect to the first end 9, of the spring element 8 is oriented in the direction toward the inlet opening 4. With a region associated with the second end 10, the spring element 8 projects into the piston element 6 and is in contact on an inner surface of an end face 7 on the piston element 6. The spring element 8 is disposed with a longitudinal axis on the longitudinal axis of piston element 6. The longitudinal axes of the piston element 6 and of the spring element 8 are disposed congruently.

(12) Piston element 6 is developed as a hollow circular cylinder with a closed end face 7. Spring element 8 is disposed within the volume encompassed by the hollow circular cylinder, wherein the spring element 8, depending on its state, which means in the non-stressed, and therewith deflected, state or stressed, and consequently compressed state, is integrated with variable proportion within the volume encompassed by the hollow circular cylinder.

(13) The spring element 8 is disposed correspondingly with the piston element 6 such that the piston element 6 in an at least nearly non-stressed state of the spring element 8 closes a flow path between the inlet opening 4 and the outlet opening 5. The piston element 6 is disposed such that it closes the device 1 according to FIG. 1A.

(14) However, the piston element 6 comprises on the shell surface indentations, not shown, as bypasses for the fluid in order to be able to conduct even in the closed state of device 1 at least a minimal mass flow of the fluid through the device 1 or past the device 1.

(15) In the stressed state of the spring element 8 the piston element 6 opens up a flow path between the inlet opening 4 and the outlet opening 5 such that a fluid to be compressed, for example a refrigerant circulating in a refrigerant circulation, flows in the direction of flow 12 through the chamber 3 of the device 1. The piston element 6 of the device 1 is displaced, depending on the mass flow conveyed by the compressor, in the direction of motion 11 and positioned depending on the ensuing equilibrium of forces.

(16) The device 1 according to FIG. 1B is opened. In the case of the opened device 1 the piston element 6 moves in the direction of motion 11 away from the inlet opening 4 and opens up at least portions of the flow cross section of the outlet opening 5 such that fluid can flow through the free flow cross section as a variable proportion of the outlet opening 5 out of the chamber 3. With the outlet opening 5 opened a high mass flow of the fluid can flow through the device 1. In the stationary state, which means at constant pressure and constant mass flow, and therewith at a consistent equilibrium of forces, the position of the piston element 6 also remains unchanged.

(17) At a large mass flow to be conveyed of the fluid to be compressed the pressure loss within the suction region, developed downstream of the outlet opening 5 in the direction of flow, of the compressor is greater than in the proximity of the inlet opening 4. The pressure difference occurring herein causes a pressure force acting onto the surface area of the end face 7 of the piston element 6, which acting pressure force moves the piston element 6 away from the inlet opening 4, With the motion of the piston element 6 the flow cross section of the outlet opening 5 is enlarged. With the enlargement of the flow cross section of the outlet opening 5, and therewith the opening of the outlet opening 5, the pressure loss within the suction region, developed succeeding the outlet opening 5 in the direction of flow, of the compressor becomes less so that the pressure difference also becomes less. At a large mass flow to be conveyed of the fluid to be compressed the pressure pulsation is low.

(18) At a low mass flow to be conveyed of the fluid to be compressed the pressure difference between the suction region, developed succeeding the outlet opening 5 in the direction of flow, of the compressor and the region of the inlet opening 4 is low such that the piston element 6 through the prestress force of the spring element 8 is moved in the direction toward the inlet opening 4 whereby the flow cross section of the outlet opening 5 is decreased. At the same time the fluid flows through the indentations, not shown, developed as bypasses on the shell surface of the piston element 6 and the outlet opening 5 into the suction region. With the low mass flow to be conveyed of the fluid to be compressed higher pressure pulsations occur. The pressure pulsations are damped through an abrupt change of the flow cross section between inlet opening 4 and the suction region. The device 1 acts as a sound absorber.

(19) In each of FIG. 2A to 2C a device 1 according to the invention for damping pressure pulsations for a compressor is shown within the chamber 3 encompassed by the housing 2 in sectional representation. In FIG. 2A the device 1 is depicted in a first end position, while the device 1 according to FIG. 2B is shown in its disposition in an intermediate position and in FIG. 20 it is shown in a second end position.

(20) The device 1 according to FIG. 2A to 2C differs from the device 1 from FIGS. 1A and 1B in particular in the implementation of the piston element 6. Identical elements of devices 1, 1 are identified by identical reference numbers.

(21) The chamber 3 is encompassed by housing 2 whose wall comprises an inlet opening 4 as well as an outlet opening 5. The compressor, in particular the device 1, is connected across the inlet opening 4 with the low-pressure side of the refrigerant circulation. The outlet opening 5 establishes the connection to the suction region of the compressor.

(22) With the piston element 6 disposed within the chamber 3 and movable in the direction of motion 11 the chamber 3 is divided, for one, into a first chamber volume 3a and a second chamber volume 3b as well as, for another, the dimensions of the chamber volumes 3a, 3b as well as also the flow cross section of the outlet opening 5 are controlled, Herein a first end face 7 of piston element 6 is oriented toward the inlet opening 4.

(23) In a first end position according to FIG. 2A the piston element 6 is positioned at a minimal distance from the inlet opening 4, the flow cross section of the outlet opening 5 is closed, the first chamber volume 3a is minimal, while the second chamber volume 3b has maximal value. The flow cross section of the outlet opening 5 and the first chamber volume 3a have each, in a second end position according to FIG. 20, maximal values since the piston element 6 is disposed at a maximal distance from the inlet opening 4. The second chamber volume 3b is minimal.

(24) Between the piston element 6 and the wall of housing 2 is disposed the spring element 8 implemented, for example, as a helical spring, in particular as a compression spring. The first end 9 of the spring element 8 is herein in contact on the end wall of housing 2, while the second end 10, implemented distally to the first end 9, of spring element 8 is oriented in the direction toward the inlet opening 4 and disposed in contact on a second end face 13 of piston element 6.

(25) Piston element 6 is developed as a hollow circular cylinder with two, at least partially closed, end faces 7, 13, which are disposed at ends, distal with respect to each other, of the shell surface of the hollow circular cylinder. The shell surface of piston element 6 is closed over its entire surface, while in each end face 7, 13 at least one through-opening 14, 15 is provided for the fluid to be compressed. The through-openings 14, 15 of end faces 7, 13 of piston element 6 establish each a fluidic connection of the environment of the piston element 6, in particular of chamber 3, with the volume encompassed by the wall of the hollow circular cylinder-shaped piston element 6.

(26) In the first end position, and therewith in an at least nearly non-stressed state of spring element 8 according to FIG. 2A, the piston element 6 is disposed such that it closes off a direct flow path developed between the inlet opening 4 and the outlet opening 5. The fluid introduced through the inlet opening 4 into the first chamber volume 3a flows in the direction of flow 12 exclusively through the through-opening 14, developed in the first end face 7 of piston element 6, into the interior of the piston element 6 as well as through the through-opening 15, developed in the second end face 13, out again of the piston element 6 into the second chamber volume 3b and is subsequently conducted through the outlet opening 5 into the suction region of the compressor. The device 1 is closed.

(27) In an intermediate state piston element 6, and therewith in a partially stressed state of spring element 8 according to FIG. 2B, the piston element 6 clears a portion of the flow cross section of outlet opening 5, which means it clears a direct flow path between the inlet opening 4 and the outlet opening 5. The fluid to be compressed, for example the refrigerant circulating in the refrigerant circulation, flows in the direction of flow 12 into the first chamber volume 3a of device 1. During its flow through the first chamber volume 3a the mass flow of the fluid is divided into a first mass subflow and a second mass subflow, with the first mass subflow being conducted through the first chamber volume 3a, along the direct flow path through the free flow cross section of outlet opening 5 into the suction region of the compressor, while the second mass subflow is conducted through the through-opening 14, developed in the first end face 7 of piston element 6, into the interior of piston element 6 as well as through the through-opening 15, developed in the second end face 13, into the second chamber volume 3b as well as subsequently through the outlet opening 5 into the suction region of the compressor. In the suction region the mass subflows are again mixed with one another.

(28) In the second end position, and therewith in a stressed state of spring element 8, according to FIG. 2C the piston element 6 is disposed such that it clears at least to a large extent the direct flow path developed between the inlet opening 4 and the outlet opening 5. The fluid conducted through the inlet opening 4 into chamber 3 flows in the direction of flow 12 through the first chamber volume 3a, along the direct flow path through the free flow cross section of outlet opening 5 into the suction region of the compressor. Device 1, in particular the outlet opening 5, is opened such that a high mass flow of the fluid can flow through the device 1.

(29) In the case of device 1 acting as a sound absorber, the pressure pulsations are also damped through an abrupt change of the flow cross section between the inlet opening 4 and the suction region. The damping effect occurs primarily in operating states with a low mass flow to be conveyed, and therewith at a low load of the compressor, which are to be seen as highly critical with respect to pressure pulsations in the motor vehicle, as well as at closed device 1.

(30) With closed or nearly closed device 1, such as in the case of configurations in the first end position according to FIG. 2A or in an intermediate position according to FIG. 2B, the fluid flows to a large proportion through the through-openings 14, 15, and therewith through the piston element 6, wherein the transmission-loss performance is increased, which damps the pressure pulsations that are propagated from the suction opening of the compressor into the refrigerant line of the refrigerant circulation. The noise emissions or their propagation into the passenger compartment are prevented.

(31) Device 1 is herein preferably disposed on the suction side of the compressor, but alternatively could also be implemented on the pressure side of the compressor.

(32) Through the piston element 6, integrated in the device 1 as a reflection damper with defined volume, the pressure pulsations with the consideration of available installation space limitations are specifically and selectively decreased in a predetermined frequency range.

(33) The piston element 6 can, for example, be implemented of Teflon.

(34) In FIG. 3A is shown in sectional representation a piston element 6 of a device 1 according to the invention for damping pressure pulsations for a compressor. In FIG. 3B are depicted transmission losses as a function of the frequency based on simulation calculations and measurements for a device 1 with a certain piston element 6.

(35) Depending on the frequency to be damped and the available installation space, the integrated piston element 6 is laid out by means of the following formula (Source: Munjal, M. L. Acoustics of Ducts and Mufflers, New York: Wiley-Interscience, 1987):

(36) $D_{\mathrm{TL}}=10\log \left(\frac{{\left({}_A+{}_E\right)}^2{\cos }^2\left(\mathrm{kL}\right)+{\left(1+{}_A{}_E\right)}^2{\sin }^2\left(\mathrm{kL}\right)}{4{}_A{}_E}\right)$$\mathrm{with}{}_A=\frac{S}{S_A}\mathrm{and}{}_E=\frac{S}{S_E}\mathrm{and}k=\frac{w}{c}=\frac{2}{}.$

(37) The available installation space is given by the inner diameter d of chamber 3 according to FIG. 2C. D.sub.TL equates to the transmission loss of the piston element 6 and consequently to the damping in the closed state of the flow cross section of outlet opening 5. The inner volume of the hollow cylinder-shaped piston element 6 is defined on the basis of the length L as well as the cross sectional area S. Herein are S.sub.E the cross sectional area of the through-opening 14 for the inflow into the piston element 6 and S.sub.A the cross sectional area of the through-opening 15 for the outflow from piston element 6.

(38) The formula for the transmission loss D.sub.TL as a measure of the reduction of the pressure pulsations applies in particular for the closed piston element 6 with the through-openings 14, 15 in the particular end faces. Through the piston element 6 with the two through-openings 14, 15 the pressure pulsations experience a reduction at the level of the transmission loss D.sub.TL.

(39) In FIG. 3B the simulation values 16, which means the values obtained from simulation calculation, and the associated measurement values 17 of device 1 are compared.

(40) With increased stress of spring element 8 the piston element 6 can, during operation with low mass flows, be maintained in the first end position according to FIG. 2A, which requires an intentional objective-oriented layout.

(41) The closed piston element 6, only developed with the two through-openings 14, 15, acts as a reflection sound absorber in order to increase the pressure pulsation damping performance. The improved propagation loss of the device 1 effects herein no noticeable change of the conveyed mass flow.