Radial-piston compressor
Patent Information
- Application Number
- EP2024704138
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-13
- Filing Date
- 2024-02-07
- Publication Date
- 2025-12-24
AI Technical Summary
Radial piston compressors face challenges in reducing installation space while maintaining delivery capacity, as increasing the number of pistons leads to collision issues and requiring larger diameters, and existing solutions like chamfers compromise guide length or increase installation space.
Implementing pistons with optimally angled chamfers to maximize guide length and using specific combinations of piston number, pole pairs, and housing screw connections to improve acoustic behavior and reduce sound pressure levels.
The solution allows for a more compact radial piston compressor design with improved piston guidance and reduced acoustic noise, maintaining performance while minimizing installation space and enhancing operational quietness.
Smart Images
Figure EP2024052967_22082024_PF_FP
Abstract
Description
[0001] Radial piston compressor
[0002] The present invention relates to a radial piston compressor according to the preamble of claim 1.
[0003] A radial piston compressor is a fluid power component. Unlike an axial piston pump, this compressor has at least one piston-working chamber combination arranged radially and perpendicular to the drive shaft. The piston's displacement or reciprocating motion is usually driven by an eccentric shaft. Typically, a radial piston compressor comprises several piston-working chamber combinations that extend radially from the drive shaft, particularly the eccentric shaft, in a star-shaped configuration.
[0004] Radial piston compressors are used, for example, as radial piston compressors for coolants in air conditioning systems of motor vehicles, especially in electrically powered motor vehicles.
[0005] A piston-working chamber combination essentially comprises a working chamber, also called a cylinder, and a piston that moves up and down within the working chamber. The piston has a central geometric piston axis that coincides with the piston's direction of travel. In a radial piston compressor with an eccentric shaft, the piston has a contact surface on its side facing the eccentric shaft, against which the eccentric disc impacts or rests during rotation of the eccentric shaft. The eccentric shaft has an axis of rotation about which the eccentric shaft is rotated. When the eccentric impacts the contact surface, the piston moves upwards, compressing a medium in the working chamber and thus increasing pressure and force.
[0006] A compact design is particularly advantageous when using radial piston compressors in motor vehicles.
[0007] If the radial installation space of the radial piston compressor is to be further reduced without reducing the delivery capacity, the number of pistons could be increased to 7, for example. While maintaining the same delivery volume (as with 6 pistons), the piston diameter can be reduced. As the number of pistons increases, collision problems arise at the point of closest contact between adjacent pistons. To generate the most uniform delivery flow possible - with minimal pressure pulsations - a piston count of at least five or more pistons should be aimed for. However, since the radial installation space of the entire radial piston compressor should remain as small as possible, the diameter of the eccentric, through which the pistons perform their lifting function, must also be kept as small as possible.For a piston according to the state of the art, which has a continuous outer diameter, this restriction with the requirement for a simultaneously larger piston diameter or an increase in the number of pistons is not feasible, since the pistons would then collide with each other in the position close to the bottom dead center.
[0008] State-of-the-art solutions are known that counteract piston collision in the "critical position" by incorporating a chamfer on the piston base. However, the introduction of the chamfer simultaneously reduces the length of the piston guide in the cylinder bore. To increase the guide length again, the piston and, accordingly, the cylinder bore would have to be enlarged, which in turn leads to an increase in the radial installation space.
[0009] This is where the present invention comes in and sets itself the task of proposing an improved radial piston compressor, in particular a radial piston compressor that can be designed more compactly with the same or similar performance data.
[0010] According to the invention, this object is achieved by a radial piston compressor having the characterizing features of claim 1. By providing each piston with a piston base, each piston base being equipped with at least one circumferential chamfer or two chamfers, the chamfer or chamfers assuming a chamfer angle with respect to the longitudinal axis of the piston, the chamfer angle being configured such that it enables the greatest possible guide length of the piston within the working chamber in the region of closest contact with the adjacent piston, an improved radial piston compressor, in particular a compact radial piston compressor, can be provided. The core idea is to provide the chamfer on the piston base with an "optimal" chamfer angle, which leads to a uniformly minimal distance in the region of closest contact between adjacent pistons and thereby enables the greatest possible guide length of the piston(s).
[0011] Further advantageous embodiments of the proposed invention emerge in particular from the features of the subclaims. The subject matter or features of the various claims can, in principle, be combined with one another as desired. In an advantageous embodiment of the invention, the chamfer angle can be provided to correspond to 3607 number of pistons / 2. An advantageous solution for the length and angle of the piston base, i.e., an optimal chamfer angle at the piston base, results from "Optimal chamfer angle = 3607 number of pistons / 2". If an optimal chamfer angle is implemented, the surfaces of the chamfers of adjacent pistons are parallel to one another - at the closest intersection. This results in reliable piston guidance while simultaneously requiring a small radial installation space.
[0012] In a further advantageous embodiment of the invention, it can be provided that the longitudinal axes of the pistons lie in one plane.
[0013] In a further advantageous embodiment of the invention, it can be provided that pistons / cylinders are evenly distributed over the circumference.
[0014] In a further advantageous embodiment of the invention, it can be provided that additional edge rounding is provided at the transition from the piston base chamfer to the piston base.
[0015] The present invention further relates to a radial piston compressor according to the preamble of claim 6 and / or 7.
[0016] Further disadvantages have become known in connection with radial piston compression.
[0017] In an electrically driven radial piston compressor, the selection of a suitable number of pistons depends not only on the desired displacement (piston stroke, piston diameter, number of pistons), but also on other component groups with a “multiplicity” of individual components.
[0018] These are determined by the geometry / design of the electric motor, for example, the number of coils / windings; the number of pole pairs; the number of magnets. For example, there may be eight pole pairs, but they are always an even multiple of two.
[0019] Another size with a multitude of individual components is the housing screw connection. The housing screw connection is intended to axially clamp the design-related housing components together so that no refrigerant is released into the environment under all operating conditions and test requirements. It must therefore fulfill a sealing function. The required contact force through the screw connection must be large enough to counteract the compressive force that would force the housings apart. The screw connections are logically placed in the angle bisector "between" the pistons or cylinders, individually or in pairs. In the example of a radial piston compressor with 7 pistons, 2x7 = 14 M6xl00 screws are arranged to fulfill the task. 7x M8 screws do not achieve the required contact force; 7x M10 screws do achieve the required contact force, but they increase the radial installation space enormously. This meansThe number of housing screw connections is linked to the number of pistons / cylinders (equal to or a multiple of the number of pistons) and the number of pole pairs. As the name suggests, this is an even-numbered size.
[0020] It is therefore provided that the radial piston compressor comprises a number of pistons, the drive device being designed as an electric machine comprising a number of pole pairs, the radial piston compressor comprising an at least two-part housing, the housing components of which are connected by a number of housing screw connections. Preferably, the radial piston compressor comprises a housing and a housing cover, which are connected to one another by the housing screw connections.
[0021] The piston-working chamber combinations and the number of poles of the electrical machine are excitation components that influence the acoustic behavior of the radial piston compressor through excitation events such as pressure peaks in the working chamber, changes between the pole pairs, etc.
[0022] A further object of the present invention is to propose an improved radial piston compressor, in particular to propose a radial piston compressor which is designed to be quieter during operation with the same or similar performance data.
[0023] According to the invention, this object is achieved by a radial piston compressor with the characterizing features of claim 6 and / or 7. This is achieved by selecting certain preferable combinations of the number of pistons, the number of pole pairs of the electric motor, and the number (including the dimensions) of the housing screw connections that are expected to improve the acoustic behavior of the overall system. The core idea here is to define a suitable combination of the number of pistons, the number of housing screw connections, and the number of pole pairs that are favorable with regard to the acoustic effects or the acoustic radiation behavior of the entire compressor. What is new in particular is that certain preferable combinations of the number of pistons, the number of pole pairs of the electric motor, and the number (including the dimensions) of the housing screw connections are defined that are expected to improve the acoustic behavior of the overall system.
[0024] Alternatively or additionally, the excitation events per revolution from the various excitation components can be different, providing a radial piston compressor that is designed to be quieter during operation with the same or similar performance data. In other words, to avoid acoustic abnormalities, the excitation events per revolution from the various excitation components (e.g., pressure curves with 7 pistons = 7x per revolution; excitation from an electric drive - number of pole pairs 8 = 8x per revolution) should be as different as possible.
[0025] This can reduce the acoustic effects (sound pressure level) of the entire system and thus lead to improved acoustic behavior in the vehicle.
[0026] Further advantageous embodiments of the proposed invention emerge in particular from the features of the subclaims. The subject matter and features of the various claims can, in principle, be combined with one another in any desired way.
[0027] In an advantageous embodiment of the invention, it can be provided that the radial piston compressor is an electrically driven radial piston compressor.
[0028] In a further advantageous embodiment of the invention, it can be provided that the drive device designed as an electric machine comprises a slot-pole pair combination, in particular permanently excited, separately excited or self-excited electric motors.
[0029] In a further advantageous embodiment of the invention, it can be provided that the piston-working chamber combinations are evenly distributed over the circumference of the radial piston compressor, in particular that the pistons of the radial piston compressor are evenly distributed. In a further advantageous embodiment of the invention, it can be provided that the housing screw connections are arranged individually or in pairs in the angle bisector between the piston axes.
[0030] In a further advantageous embodiment of the invention, it can be provided that a distance as equal as possible, in particular equal, is provided between the screws, seen on the circumference of the screw hole circle, in order to generate a uniform contact pressure on the surface seal (axially between the housing components).
[0031] In a further advantageous embodiment of the invention, it can be provided that further combinations of number of pistons, number of pole pairs and / or number of screws are used.
[0032] In a further advantageous embodiment of the invention, it can be provided that screw connections deviating from the standard (size M7, or thread pitch) are used.
[0033] In a further advantageous embodiment of the invention, it can be provided that the strength class of the screws (8.8; 10.9; 12.9 oa) can be varied.
[0034] In a further advantageous embodiment of the invention, it can be provided that the type of housing screw connection (screw head shape, screw shaft, expansion screws, stud bolts with nuts, etc.) can be varied.
[0035] In a further advantageous embodiment of the invention, it can be provided that the type and material of the magnets of the electric motor can be varied.
[0036] In a further advantageous embodiment of the invention, it can be provided that the type of electrical machine (optionally also asynchronous machine or separately excited synchronous machine)
[0037] The present invention further relates to a radial piston compressor according to the preamble of claim 19.
[0038] Further disadvantages have become known in connection with radial piston compressors. A further object of the present invention is to propose an improved radial piston compressor, in particular a radial piston compressor that is designed to be quieter during operation while maintaining the same or similar performance data.
[0039] According to the invention, this object is achieved by a radial piston compressor with the characterizing features of claim 19. The invention proposes a suitable combination of the number of pistons, piston diameter, and piston stroke, in which the exciting force component from the pressure curves of the compression processes represents an optimum. In other words, it is intended that certain preferred combinations of the number of pistons, piston diameter, and piston stroke should lead to an optimal excitation function on the eccentric at selected operating points. A specific stroke / diameter ratio with the associated number of pistons should be selected, adapted to the compression process.
[0040] This reduces the acoustic impact, particularly the sound pressure level, of the entire system, thus contributing to improved acoustic performance in the vehicle. In particular, it also results in a longer bearing life of the eccentric bearing and / or reduced torque fluctuations of the compressor, thus improving controllability.
[0041] Further features and advantages of the present invention will become clear from the following description of preferred embodiments with reference to the accompanying drawings.
[0042] Fig. 1 a radial piston compressor in a side sectional view;
[0043] Fig. la a radial piston compressor in a sectional view;
[0044] Fig. 2 is a schematic representation of a radial piston compressor, showing the pistons with larger diameter and small eccentric and the resulting collision;
[0045] Fig. 3a to 3e a schematic representation of a radial piston compressor and details of a radial piston compressor, in particular chamfer on the piston base;
[0046] Fig. 4 possible combinations of number of pistons, number of pole pairs of the electric motor and required number / dimension of housing screw connections;
[0047] Fig. 5 useful combination variants with the number of pistons “5”;
[0048] Fig. 6 useful combination variants with seven and eight pistons;
[0049] Fig. 7 useful combination variants with nine pistons;
[0050] Fig. 8 Cylinder pressure curve over cylinder volume - compression phases,
[0051] Fig. 9 Pressure curve per piston;
[0052] Fig. 10 superimposed piston pressure curves of a five-piston radial piston compressor;
[0053] Fig. 11 resulting radial load from the superposition of the pressure curves of 5 and 6 pistons;
[0054] Fig. 12 resulting radial force at an operating point for different numbers of pistons;
[0055] Fig.13 Principle representation of eccentric bearing loads under different operating conditions.
[0056] The following reference symbols are used in the figures:
[0057] A piston axis
[0058] R axis of rotation
[0059] F chamfer
[0060] Fl first phase
[0061] F2 second chamfer a chamfer angle
[0062] Drive angle AW
[0063] L Guide length Z Number of cylinders / number of pistons
[0064] V Number of screw connections P Number of pole pairs
[0065] M Dimension of the screw connection
[0066] D piston diameter
[0067] H piston stroke
[0068] K Piston collision
[0069] 1 drive device
[0070] 2 compaction device
[0071] 3 pole
[0072] 4 screw connection
[0073] 5 housings
[0074] 6 coupling link / swivel segment
[0075] 21 Drive shaft
[0076] 22 eccentric
[0077] 23-23”” piston-working chamber combinations
[0078] 41 Screw
[0079] 42 through hole
[0080] 43 threaded hole
[0081] 51 Housing cover
[0082] 52 fuselage housing
[0083] 231 Working chamber (cylinder bore)
[0084] 232 pistons
[0085] 2321 piston base
[0086] 2322 Edge rounding. Features and details described in connection with a method naturally also apply in connection with the device according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other. Furthermore, a method according to the invention that may be described can be carried out with the device according to the invention.
[0087] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a" and "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of the recited features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed elements.
[0088] First, reference is made to Figs. 1 and 1a.
[0089] Figure 1 shows a radial piston compressor with piston designs, in particular a compact embodiment of a radial piston compressor, with six pistons 232 for use with the refrigerant CO2. Coupling elements 6—also called pivot segments—can be provided between the eccentric bearing outer diameter and the piston base.
[0090] A radial piston compressor essentially comprises a drive device 1 and a compression device 2.
[0091] The drive device 1 can, for example, be an electric motor.
[0092] The compression device 2 comprises a drive shaft 21 with an eccentric 22, as well as piston-working chamber combinations 23-23"" arranged radially around the drive shaft. The drive shaft 21 with the eccentric 22 can also be referred to as an eccentric shaft. A piston-working chamber combination 23 essentially comprises a working chamber 231, also called a cylinder, and a piston 232, which is moved up and down in the working chamber 231. The piston 232 has a central geometric piston axis A, which coincides with the displacement direction of the piston 232. In a radial piston compressor with an eccentric shaft 21, 22, the piston 232 comprises a contact surface on its side facing the eccentric shaft, against which the eccentric disc 22 strikes or rests during the rotation of the eccentric shaft. The eccentric shaft has an axis of rotation R around which the eccentric shaft is rotated.When the eccentric hits the contact surface, the piston moves upwards and a medium located in the working chamber 231 is compressed, thus leading to an increase in pressure and force.
[0093] In the following, particular reference is made to Fig. 2.
[0094] Fig. 2 schematically shows that a piston collision K can occur if two adjacent pistons are at a lower low point or near the lower low point and no suitable measures are taken against this.
[0095] In the following, particular reference is made to Figs. 3a to 3e.
[0096] The pistons 232 used here have a piston base 2321, i.e., a region of the piston 232 facing the drive shaft 21. The piston base 2321 is equipped with a circumferential chamfer F or two chamfers, in particular a first chamfer F1 and a second chamfer F2, which form or form an angle, hereinafter referred to as chamfer angle α, with the longitudinal axis K of the piston. Accordingly, the first chamfer F1 forms a chamfer angle cti, and the second chamfer F2—in the case of two chamfers—forms a chamfer angle α2 with the piston axis A.
[0097] In the case of a circumferential chamfer, the result is essentially a conical piston base. The chamfer angle is referred to as chamfer angle a. In the case of two chamfers, the result is essentially two surfaces set at the corresponding angle.
[0098] The chamfer itself is preferably designed as a flat surface. The chamfer angles ai and a2 are preferably equal, so that in the following, reference is made to a chamfer angle a. According to the invention, an optimal chamfer angle a is provided at the piston base 2321, which allows the greatest possible guide length L of the piston within the cylinder bore 231 in the region of closest contact between adjacent pistons 232.
[0099] The guide length L of the piston 232 is the section or length of the piston 232 with which the piston can be guided in the working chamber.
[0100] The best solution for the length and angle of the piston base chamfer Fl, F2, i.e., an optimal chamfer angle a at the piston base 2321, is calculated as follows: "Optimal chamfer angle a = 3607 number of pistons / 2." The number of pistons is the number of pistons arranged side by side in the circumferential direction of the radial piston compressor. If an optimal chamfer angle a is implemented, the surfaces of the chamfers Fl, F2 of adjacent pistons are parallel to each other at the closest intersection. This results in reliable piston guidance while simultaneously maintaining a small radial installation space.
[0101] Some examples are shown in Fig. 3, in particular Fig. 3a and 3b show representations with a small chamfer Fl or F2 on the piston base 2321 with the larger guide length and Fig. 3c and 3d show the larger chamfer Fl or F2 on the piston base, which is designed so large that no collision occurs, but at the same time reduces the guide length with the same total piston length.
[0102] In Fig. 3e, a chamfer angle a is shown in relation to the longitudinal axis K of a piston 232.
[0103] It is further preferably provided that the longitudinal axes of the pistons, i.e. their piston axes A, lie in one plane.
[0104] It is further preferably provided that pistons / cylinders, i.e. piston-working chamber combinations, are provided that are evenly distributed over the circumference, ie that the angle between adjacent piston axes A is the same for all.
[0105] Furthermore, preferably low installation space requirements are provided, which causes the risk of collision between adjacent pistons.
[0106] Preferably, additional edge roundings 2322 can be provided at the transition of the piston base chamfer Fl or F2 to the piston base 2321. Preferably, the size of the respective piston diameter / cylinder bore diameter, number of pistons, and / or chamfer length at the piston base can vary.
[0107] Different chamfer lengths can also be provided on the piston base 2321 on both sides if the piston axis A is offset, in particular if the cylinder bores are offset such that the axes do not intersect or the opposing cylinders are not on the same axis, or if the piston base 2321 has a different chamfer in the section along the eccentric axis than in the cross section.
[0108] Reference is made below to Figures 4 to 7.
[0109] With regard to the basic features of the radial piston compressor, reference can be made to Figs. 1 and 1a and the relevant description.
[0110] A radial piston compressor comprises a drive device 1 designed as an electric machine with a corresponding number of poles 3, i.e., a number of poles. Two poles are usually combined to form pole pairs. The radial piston compressor also comprises screw connections 4. The screw connections generally comprise a screw 41, a through-hole 42, and a corresponding threaded hole 43 into which the screw 41 can be inserted or screwed. A housing 5 of the radial piston compressor, which consists of at least two parts, is connected to one another via the screw connection 4. The housing preferably comprises a housing cover 51 and a body housing 52, which are connected to one another via the screw connections 4.
[0111] The housing screw connection 4 is intended to axially clamp the design-related housing parts 51, 52 together so that no refrigerant is released into the environment under all operating conditions and test requirements. It must therefore fulfill a sealing function. The required contact force exerted by the screw connection 4 must be large enough to counteract the compressive force that would force the housing parts 51, 52 apart. The screw connections 4 are logically placed in the angle bisector "between" the pistons or cylinders, i.e., the piston-working chamber combinations 23, individually or in pairs.
[0112] The radial piston compressor also has a number of piston-working chamber combinations 23, and accordingly a corresponding number of pistons 232 or working chambers 231. Additionally or alternatively, it can be provided here that the radial piston compressor forms excitation components through the piston-working chamber combinations 23 and the poles 3 of the electric machine, wherein the excitation components are characterized by excitation events, such as pressure peaks in the working chamber 231 and a change between the pole pairs 3, which influence the acoustic behavior of the radial piston compressor.
[0113] Below, particularly in Figures 4 to 7, advantageous combinations of the number of cylinders Z, the number of pole pairs P, the number of V, and the dimensions M of the housing screw connections are listed and explained. Generally, for the "acoustics" criterion, variants with the highest possible "kgV" are preferable.
[0114] The LCM is the product of the number of pistons or cylinders Z and the number P of pole pairs of the drive system configured as an electric machine, especially for prime numbers. For 6 screws and 8 pole pairs, the lowest common multiple (LCM) is not 6 x 8 = 48 but 24 (4 x 6 = 24 and 3 x 8 = 24).
[0115] On the other hand, some of these variants have a large number of components (pistons; pole pairs) and are therefore not preferable in terms of manufacturing costs.
[0116] Fig. 4 shows possible combinations of the number of pistons Z, the number of pole pairs P of the drive device designed as an electric machine, and the required number V or dimension M of housing screw connections 4 in a design path. The forces to be withstood by the screw connection are significantly influenced by its inner diameter Di or the resulting pressurized area. The number of pistons Z can be influenced by the required displacement HVol and the radial installation space. The number of magnets or pole pairs P varies according to requirements, with a larger number of pole pairs P meaning less "ripple," i.e., smaller / less cogging torque, but is more expensive.
[0117] Fig. 5 shows that with a pole pair number of P=8 (combination "1"), an acceptable "kgV" of 40 can be achieved with a small number of components. With P=12 pole pairs (combination "2"), the "kgV" is 60.
[0118] Figure 6 shows that with seven pistons, each of the selected pole pair numbers P (8, 10, 12) can achieve a high "kgV" (lower limit) coefficient. With eight pistons, only a combination of 10 pole pairs is acceptable. With a pole pair number P=12, a "kgV" of 24 results, meaning that every second revolution of the compressor would result in a "simultaneous" excitation from the piston drive and the electric motor, which would lead to "poor" acoustics.
[0119] Fig. 7 shows that a large "kgV" is achieved with nine pistons and a pole pair number of P=8 or 10. However, this combination also requires a large number of components for the overall system.
[0120] According to the invention, it is provided that certain preferred combinations of the number of pistons or cylinders Z, the number of pole pairs P of the electric motor and the number V including the dimensions M of the housing screw connections are selected, which are expected to improve the acoustic behavior of the overall system.
[0121] Alternatively or additionally, it can be provided that the excitation events per revolution are different from the different excitation components.
[0122] This makes it possible to create a radial piston compressor that is quieter during operation while maintaining the same or similar performance data. In other words, to avoid acoustic abnormalities, the excitation events per revolution from the various excitation components (e.g., pressure curves with seven pistons = 7x per revolution; excitation from an electric drive - number of pole pairs 8 = 8x per revolution) should be as different as possible.
[0123] The radial piston compressor described here is characterized in particular by the following features.
[0124] It is preferably an electrically driven radial piston compressor, i.e. the drive device is designed as an electric machine.
[0125] It is preferably an electrical machine with a slot-pole pair combination of either permanent magnet, separately excited or self-excited electric motors.
[0126] Preferably, uniformly distributed pistons or piston-working chamber combinations are provided for the radial piston compressor. Preferably, the housing screw connections 4 are arranged individually or in pairs in the angle bisector between the piston axes A.
[0127] Preferably, a distance as equal as possible, preferably the same distance, seen on the circumference of the screw hole circle, between the screws 41 is provided in order to generate a uniform contact pressure on the surface seal, in particular axially between the housing components 51, 52.
[0128] In particular, variations or further combinations of the number of pistons Z, the number of pole pairs P and / or the number of screws V are conceivable.
[0129] In particular, screw connections 4 that deviate from the standard, in particular size M7, or thread pitch, are conceivable.
[0130] In particular, variations in the strength class of the screws 41, for example strength class 8.8; 10.9; 12.9 or similar, are conceivable.
[0131] In particular, variations are conceivable with regard to the type of housing screw connection 4, in particular screw head shape, screw shaft, expansion screws, stud bolts with nuts, etc.
[0132] Variations in the type and material of the magnets of the electric motor are conceivable.
[0133] Variations in the type of electrical machine are conceivable, in particular either an asynchronous machine or a separately excited synchronous machine.
[0134] Reference is made below to Figs. 8 to 13d.
[0135] With regard to the basic features of the radial piston compressor, reference can be made to Figs. 1 and 1a and the relevant description.
[0136] The radial piston compressor outlined here is characterized in particular in that the radial piston compressor has a number of pistons 232, wherein the pistons 232 have a piston diameter D, wherein the pistons have a piston stroke H. Fig. 8 schematically shows a cylinder pressure curve over the cylinder volume, in particular compression phases. In an electrically driven radial piston compressor, the selection of a suitable number of pistons Z depends not only on the desired displacement volume, in particular piston stroke H, piston diameter D, number of pistons Z, but also on its force excitations in interaction over the individual compressor stroke processes. Each stroke movement of a radial piston compressor follows the two-stroke principle, which includes the intake phase, compression phase, discharge phase and expansion phase.
[0137] Figure 9 shows a pressure curve for each piston. During the compression phase, discharge phase, and expansion phase, a pressure force acts on the piston, which can be represented as a cylinder pressure curve ZD over time or the angle / drive angle AW or the cylinder volume ZV of the compression process.
[0138] Figure 10 schematically shows superimposed piston pressure curves of a five-piston radial compressor. Similar to the excitation function of an internal combustion engine, the cylinder pressure curves ZD are superimposed, resulting in an exciting force component F on the eccentric 22 of the radial piston compressor.
[0139] Fig. 11 schematically shows a resulting real load from the superposition of the pressure curves of five and six pistons 232. For one cylinder 231, there is a continuous pulse once per revolution. For two cylinders, a pulse occurs twice per revolution, etc. The optimal way to excite the system would be a superposition of pulses which, due to their length, shape, and number of exciting radial force components, form an exactly constant total force without superimposed amplitude. The number of pistons must therefore be selected so that the compression processes of the individual pistons do not overlap but also do not overlap. However, since, regardless of the combination, depending on the pressure level, the pressure curves can either overlap or not overlap, the resulting force amplitude is crucial for exciting the system.If you use smaller pistons with lower surface pressure forces for the same compressor displacement, you need a larger number of pistons. This, in turn, results in smaller resulting force amplitudes.
[0140] Fig. 12 schematically illustrates a resulting radial force F at an operating point for different piston numbers (numbers on the curves). Certain combinations of piston number and stroke / bore ratio lead to an almost complete cancellation of the exciting amplitude at selected operating points due to the shape, length, and number. For example, Fig. 12 shows a minimum of the exciting amplitude for a combination of seven pistons, a 16 mm piston diameter D, and a stroke H of 8 mm. Despite a higher number of pistons, this minimum system excitation is not achieved by the system with 8 pistons.
[0141] Eccentric bearing loads are plotted under different operating conditions and with different numbers of pistons in Figs. 13a to 13d. The load on the eccentric drive at different speeds, pressure ratios, and numbers of pistons is shown in Figs. 13a to 13d. The basis for this is the same compressor displacement, which varies by the number of pistons and the piston diameter D at the same stroke H. It is clearly evident that with seven or more pistons, there is a significant reduction in the radial loads on the eccentric compared to variants with five or six pistons. The exciting forces and their amplitudes decrease significantly, which leads to improved NVH (noticeable and audible vibration) behavior and thus to greater acceptance by the end customer. A radial piston compressor with at least seven pistons, ideally eight or nine pistons, represents a system with favorable excitation characteristics in this case.
[0142] Furthermore, the lower amplitudes reduce the bearing load on the eccentric drive. This allows for either the installation of a smaller bearing or a longer service life of the eccentric bearing.
[0143] Especially at low pressure ratios, seven pistons are optimal due to the favorable overlap of the cylinder pressure curves. This favors compressor operation at low pressure ratios, since, purely mechanically, a resulting low torque fluctuation can be expected. Due to the compressor's low torque fluctuation, the electric motor has better control options and is less excited.
[0144] The invention proposes a suitable combination of the number of pistons Z, piston diameter D, and piston stroke H, in which the exciting force component from the pressure curves of the compression processes represents an optimum. In other words, it is intended that certain preferable combinations of the number of pistons Z, piston diameter, and stroke H of the piston 232 should lead to an optimal excitation function at the eccentric 22 at selected operating points. A specific stroke / diameter ratio H / D with the associated number of pistons Z should be selected, adapted to the compression process.
[0145] This reduces the acoustic impact, particularly the sound pressure level, of the entire system, thus contributing to improved acoustic performance in the vehicle. In particular, it also results in a longer bearing life of the eccentric or a bearing arranged on the eccentric disc, especially a roller bearing, and / or reduced torque fluctuations of the compressor, thus improving controllability.
[0146] The radial piston compressor is preferably an electrically driven radial piston compressor operating in two-stroke mode. An electric motor is preferably used as the drive device. Furthermore, uniformly distributed pistons 232 are preferably provided for the radial piston compressor.
[0147] Further combinations of piston number / diameter to piston number are also conceivable. Refrigerants other than CO2 are also conceivable as fluids for the radial piston compressor.
[0148] A preferred application for the radial piston compressors proposed here is in the field of air conditioning systems in motor vehicles. Accordingly, the radial piston compressor is preferably designed to compress a refrigerant or fluid, such as CO2. However, other applications and fluids are also conceivable.
Claims
Claims 1. Radial piston compressor, comprising - a drive device (1) and a compressor device (2), wherein - the compressor device (2) comprises a drive shaft (21) with an eccentric (22), wherein - at least one, preferably several, piston-working chamber combinations (23- 23 ) extend radially from the drive shaft (21), wherein - each piston-working chamber combination comprises a working chamber (231) and a piston (232) displaceable in the working chamber, wherein the piston (232) comprises a longitudinal axis (A), characterized in that - each piston (232) comprises a piston base (2321), each piston base (2321) being provided with one circumferential chamfer (F) or two chamfers (F1, F2), - the circumferential chamfer (F) or the chamfers (Fl, F2) assume a chamfer angle (a or ai, a2) with respect to the longitudinal axis (A) of the piston (232), wherein the chamfer angle (a or ai, a2) is arranged such that it enables the greatest possible guide length (L) of the piston (232) within the working space (231) in the region of the closest contact with the adjacent piston.
2. Radial piston compressor according to claim 1, characterized in that the chamfer angle (ai or a2) = 3607number of pistons (Z) / 2.
3. Radial piston compressor according to at least one of the preceding claims, characterized in that the longitudinal axes (A) of the pistons (232) lie in one plane.
4. Radial piston compressor according to at least one of the preceding claims, characterized in that pistons / cylinders (231, 232) are provided which are evenly distributed over the circumference.
5. Radial piston compressor according to at least one of the preceding claims, characterized in that additional edge roundings (2322) are provided at the transition of the chamfer (F) to the piston base (2321).
6. Radial piston compressor according to at least one of the preceding claims or the preamble of claim 1, wherein - the radial piston compressor comprises a number (V) of pistons (232), wherein - the drive device (1) is designed as an electrical machine, comprising a number of pole pairs (3), wherein - the radial piston compressor comprises at least a two-part housing (51, 52), the housing components of which are connected by a number of screw connections (4), characterized in that certain preferable combinations of the number of pistons (V), the number of pole pairs (3) of the electric machine and the number (V) including the dimensions (M) of the screw connections (4) are selected, which are expected to improve the acoustic behavior of the overall system.
7. Radial piston compressor according to at least one of the preceding claims or the preamble of claim 1, wherein - the radial piston compressor forms excitation components through the piston-working chamber combinations (23) and the pole pairs (3) of the electric machine, wherein the excitation components are characterized by excitation events, such as pressure peaks in the working chamber (231) and a change between the pole pairs (3), which have an influence on the acoustic behavior of the radial piston compressor, characterized in that the excitation events per revolution are different from the various excitation components.
8. Radial piston compressor according to at least one of the preceding claims, characterized in that the radial piston compressor is an electrically driven radial piston compressor.
9. Radial piston compressor according to at least one of the preceding claims, characterized in that the drive device (1) designed as an electric machine comprises a slot-pole pair combination, in particular it is a permanently excited, separately excited or self-excited electric motor.
10. Radial piston compressor according to at least one of the preceding claims, characterized in that the piston-working chamber combinations (23) are arranged evenly distributed over the circumference of the radial piston compressor, in particular evenly distributed pistons (232) of the radial piston compressor are present.
11. Radial piston compressor according to at least one of the preceding claims, characterized in that the arrangement of the screw connections (4) is provided individually or in pairs in the angle bisector between the piston axes (A).
12. Radial piston compressor according to at least one of the preceding claims, characterized in that a distance as equal as possible, in particular equal, is provided between the screw connections (4) as seen on the circumference of the screw hole circle in order to generate a uniform contact pressure on the surface seal, in particular axially between the housing components.
13. Radial piston compressor according to at least one of the preceding claims, characterized in that further combinations of number of pistons (Z), number of pole pairs (P) and / or number (V) of screw connections (V) are used.
14. Radial piston compressor according to at least one of the preceding claims, characterized in that screw connections (4) deviating from the standard, in particular size 7, or thread pitch, are used.
15. Radial piston compressor according to at least one of the preceding claims, characterized in that the strength class of the screws (41), in particular strength class 8.8; 10.9; 12.9 or similar, can be varied.
16. Radial piston compressor according to at least one of the preceding claims, characterized in that the type of screw connection, in particular screw head shape, screw shaft, expansion screws, stud bolts with nuts, etc., can be varied.
17. Radial piston compressor according to at least one of the preceding claims, characterized in that the type and material of the magnets of the electric motor can vary.
18. Radial piston compressor according to at least one of the preceding claims, characterized in that the type of electrical machine can vary, in particular the electrical machine can be designed either as an asynchronous machine or a separately excited synchronous machine.
19. Radial piston compressor according to at least one of the preceding claims or the preamble of claim 1, wherein - the radial piston compressor has a number (Z) of pistons (232), wherein - the pistons (232) have a piston diameter (D), wherein - the pistons (232) have a piston stroke, characterized in that a suitable combination of the number of pistons (Z), diameter (D) and stroke (H) of the pistons (232) is selected, in which the exciting force component from the pressure curves of the compression processes represents an optimum.
20. Radial piston compressor according to at least one of the preceding claims, characterized in that the radial piston compressor is an electrically driven radial piston compressor in two-stroke operation.
21. Radial piston compressor according to at least one of the preceding claims, characterized in that an electric machine is used as the drive device.
22. Radial piston compressor according to at least one of the preceding claims, characterized in that uniformly distributed pistons (232) are provided for the radial piston compressor.
23. Radial piston compressor according to at least one of the preceding claims, characterized in that further combinations of number of pistons / diameter (Z / D) to number of pistons (Z) are conceivable.
24. Radial piston compressor according to at least one of the preceding claims, characterized in that other refrigerants than CO2 are conceivable as fluid for the radial piston compressor.