Positive displacement machine

Abstract

The invention relates to a positive displacement machine, in particular a compressor, comprising: at least one variable-volume compression chamber for compressing a refrigerant, the compression chamber being formed by a stationary chamber component and a movable chamber component; and a lubrication system for lubricating movable machine components of the positive displacement machine. The lubrication system has a lubricant separator (SA) and an intermediate lubricant reservoir (SK) which is arranged downstream of the lubricant separator (SA) in the flow direction of the lubricant; the intermediate lubricant reservoir (SK) can be transferred from a filling state into a discharge state by the movement of the movable chamber component; and the intermediate lubricant reservoir (SK) can be fluidically connected or is fluidically connected, in the filling state, to the lubricant separator (SA), in particular to a lubricant tank (ST) of the lubricant separator (SA), and, in the discharge state, to the machine components to be lubricated.

Description

[0001] Displacement engine

[0002] The invention relates to a positive displacement machine, in particular a compressor. Furthermore, the invention relates to a method for operating a positive displacement machine. In particular, the invention relates to positive displacement machines for use in the air conditioning of vehicle interiors or other vehicle parts.

[0003] Positive displacement machines, especially those used for vehicle air conditioning, typically have several components that require adequate lubrication. This lubrication is usually achieved via an internal lubricant circuit within the machine. During operation, at least some of the lubricant, usually oil, enters the refrigerant and must therefore be separated after compression in a section of the machine. The separated lubricant is usually returned to the suction side of the machine. This creates an internal lubricant circulation within the machine with an internal lubricant circulation rate. The lubricant that is not separated and / or not returned enters the overall system. The amount of lubricant entering the overall system is called the external lubricant circulation rate (OCR).

[0004] In general, positive displacement compressors have variable-volume compression chambers to compress the refrigerant. These variable-volume compression chambers are usually formed by a stationary chamber component, such as a cylinder or a stationary displacement spiral. To vary the volume of the compression chamber, a movable chamber component is provided, which can be, for example, a piston or an orbiting displacement spiral. Positive displacement compressors that use pistons and cylinders as chamber components are called reciprocating compressors. Positive displacement compressors with interlocking compressor spirals are called scroll compressors.

[0005] Displacement compressors, especially those used in vehicles, operate in various modes. One mode involves their use as part of a heat pump, for example, to heat the air inside the vehicle. Another common mode is as part of a vehicle's air conditioning system, cooling the interior air. In battery-electric or hybrid-electric vehicles, such compressors can also be used as part of a battery cooling circuit. Finally, a displacement compressor might be used within a vehicle's air conditioning system primarily for dehumidifying the interior, rather than cooling it.

[0006] The aforementioned operating modes differ primarily in the way the positive displacement machine is controlled. Within each operating mode, the positive displacement machine can also be operated at different speeds.

[0007] If we consider the external lubricant circulation rate in relation to the rotational speed, it increases with increasing speed. The amount of lubricant in the overall system must therefore be particularly high to ensure lubrication of the positive displacement machine's components, especially at low speeds. This results in an excess of lubricant in the positive displacement machine at higher speeds. This excess cannot be retained within the machine. It leaves the positive displacement machine along with the refrigerant and circulates throughout the entire system. The amount of this externally circulating lubricant is referred to as the external lubricant circulation rate (OCR). Within the overall system, the externally circulating lubricant negatively impacts the heat transfer of the heat exchangers (evaporator, condenser, gas cooler), thereby reducing the overall system efficiency.

[0008] Against this background, the object of the invention is to provide a positive displacement machine that supplies a sufficient quantity of lubricant across all operating ranges while simultaneously keeping the external lubricant circulation rate low. Furthermore, it is an object of the invention to provide a method for operating such a positive displacement machine.

[0009] According to the invention, this problem is solved with regard to the displacement machine by the subject matter of claim 1 and with regard to the operating method by the subject matter of claim 10.

[0010] Specifically, the invention is based on the concept of a positive displacement machine, in particular a compressor, with at least one variable-volume compression chamber for compressing a refrigerant, which is formed by a stationary chamber component and a movable chamber component. The positive displacement machine further comprises a lubrication system for lubricating moving machine components of the positive displacement machine, wherein the lubrication system includes a lubricant separator and a lubricant intermediate storage unit. The lubricant intermediate storage unit is located downstream of the lubricant separator in the direction of lubricant flow.Furthermore, the lubricant intermediate storage can be converted from a filling state to a dispensing state by the movement of the movable chamber component, wherein the lubricant intermediate storage is fluidly connectable or fluidly connected to the lubricant separator, in particular a lubricant tank of the lubricant separator, in the filling state and to the machine components to be lubricated in the dispensing state.

[0011] Unlike known lubrication systems, in which the internal circulation rate of the lubricant is essentially independent of the rotational speed of the positive displacement machine, the invention takes the approach of setting a speed-dependent internal lubricant rate. This is achieved by the lubricant reservoir, which is preferably mechanically coupled to the movable chamber component of the positive displacement machine, so that the filling and emptying of the lubricant reservoir are controlled by the movable chamber component. The internal lubricant circulation rate is thus coupled to the rotational speed of the positive displacement machine.

[0012] The advantage of the resulting speed-dependent internal lubricant circulation rate is that a nearly ideal quantity of lubricant is provided for component lubrication in all operating conditions. This is achieved by temporarily storing a separated quantity of lubricant in a lubricant tank and supplying it to the intermediate lubricant storage as needed. This has the advantage that the separated lubricant is supplied to the mechanical components only as required, thus preventing excess lubricant. This effect results in only small quantities of lubricant leaving the positive displacement machine, and consequently, a low external lubricant circulation rate.

[0013] For controlling the positive displacement machines according to the invention, it is advantageous if the lubricant reservoir assumes the filling state and the discharge state at predetermined, independent times. These independent times can occur within the working cycles of the compression chamber. In particular, a filling and a discharge of lubricant can thus take place in one revolution or working cycle of the positive displacement machine. A working cycle can, for example, comprise two working cycles.

[0014] In particular, the filling and dispensing states can alternate at a frequency directly proportional to the rotational speed of the positive displacement machine. This direct proportional relationship between the rotational speed of the positive displacement machine and the filling and dispensing of lubricant from the intermediate lubricant reservoir means that the rotational speed of the positive displacement machine sets the decisive parameter for the internal lubricant circulation rate. Regardless of the operating point or

[0015] The operating condition of the displacement machine ensures optimal lubricant distribution or supply to the machine components of the displacement machine that need lubrication.

[0016] In a preferred embodiment of the positive displacement machine according to the invention, the lubricant reservoir assumes a closed state between the filling and dispensing states. It is particularly preferred that the lubricant reservoir is never simultaneously in fluid contact with both the lubricant separator and the machine components to be lubricated. Rather, it is preferred that the lubricant reservoir is fluid-connected either only to the lubricant separator or only to the machine components to be lubricated, particularly the suction side of the positive displacement machine, over time. This allows the internal lubricant circulation rate to be controlled precisely.

[0017] The lubricant reservoir can be integrated into the stationary and / or the movable chamber component. Embedding the lubricant reservoir in the stationary and / or the movable chamber component results in a particularly simple design for the positive displacement machine according to the invention. In particular, this avoids the need for additional components, making the implementation of the preferred embodiment of the invention especially cost-effective.

[0018] In preferred embodiments, the lubricant reservoir can be fluidly connected to the compression chamber and / or to a suction side of the positive displacement machine and / or to a bearing, in particular a plain bearing or ball bearing, of the positive displacement machine in the discharge state. It is essential to note here that a fluid connection does not necessarily require direct mechanical contact between the lubricant reservoir and the components to be lubricated. The fluid connection can also be established via appropriate lubricant lines, which is therefore preferred.

[0019] The displacement machine according to the invention can be a scroll compressor. In a scroll compressor, the stationary chamber component is preferably formed by a stationary displacement spiral and the movable chamber component by an orbiting displacement spiral. The orbiting displacement spiral preferably engages with the stationary displacement spiral, forming a volume-variable compression chamber.

[0020] Particular advantages are achieved when the lubrication system of the positive displacement machine is designed without nozzles and / or throttles. Such a positive displacement machine with a nozzle-free and / or throttle-free lubrication system is especially robust and requires little maintenance. Furthermore, the nozzle-free and / or throttle-free design of the lubrication system simplifies the tuning of the positive displacement machine for the intended application. In other words, an advantage of the positive displacement machine according to the invention is that the use of the lubricant reservoir eliminates the need for nozzles and / or throttles in the lubrication system, resulting in reduced manufacturing and maintenance costs.

[0021] A subordinate aspect of the invention relates to a method for operating a displacement machine, in particular a displacement machine described above.

[0022] The method according to the invention comprises the following steps:

[0023] Separation of lubricant from a refrigerant in a lubricant separator, in particular wherein the lubricant is collected in a lubricant tank of the lubricant separator;

[0024] Transferring the lubricant to a lubricant reservoir while it is in a filling state;

[0025] Holding the lubricant in the lubricant reservoir while it is in a closed state;

[0026] Dispensing the lubricant to machine components of the displacement machine from the lubricant reservoir while the reservoir is in a dispensing state; wherein the transfer, holding and dispensing of the lubricant takes place at independent times, and wherein the filling state, the closing state and the dispensing state of the lubricant reservoir are produced alternately, in particular independently of time, by a relative movement between a stationary chamber component and a movable chamber component of the displacement machine.

[0027] The advantages and preferred embodiments mentioned in connection with the displacement machine according to the invention apply accordingly to the operating method described here. In particular, the described operating method achieves sufficient lubrication of machine components in a displacement machine. The operating method according to the invention also advantageously results in efficient operation of the displacement machine and an increase in system efficiency.

[0028] In a preferred embodiment of the method according to the invention, the transfer, retention, and release of the lubricant are dependent on the rotational speed of the displacement machine. This links the internal lubricant circulation rate to the rotational speed of the displacement machine and ensures it is adequately adjusted in every operating mode. Essentially, the internal lubrication of the displacement machine is therefore automatic. This offers advantages when integrating the displacement machine into a vehicle's overall cooling or heating system.

[0029] The invention is explained in more detail below using an exemplary embodiment with reference to the accompanying schematic drawings. These show

[0030] Fig. 1 shows a diagram with measured values ​​of an external lubricant circulation rate under different operating conditions of a conventional scroll compressor;

[0031] Fig. 2 shows a diagram of an expected distribution of the external lubricant circulation rate under different operating conditions of a positive displacement machine according to the invention, which is preferably designed as a scroll compressor; and

[0032] Figs. 3a-3c show a schematic representation of the operation of a displacement machine according to the invention in a preferred embodiment, showing different states of the lubricant intermediate storage.

[0033] Figure 1 shows a diagram with measurement results from a conventional scroll compressor. The diagram illustrates the external lubricant circulation rate, specifically the oil circulation rate (OCR), in various operating modes of the scroll compressor. The rotational speeds were categorized into "low," "medium," and "high" speed groups. The "low" speed group, for example, can encompass drive shaft speeds of a scroll compressor from 1000 to 2000 revolutions per minute. The "medium" speed group can cover a drive shaft speed range between 2000 and 6000 revolutions per minute. The "high" speed group can be defined as drive shaft speeds between 6000 and 9000 revolutions per minute. A lubricating oil is preferably used as the lubricant. The operating modes shown in the diagram according to Figure 1 are...The operating modes that can be distinguished are: one in which the known scroll compressor is used to operate a vehicle's heat pump system (HP); another in which the scroll compressor is used as part of a vehicle air conditioning system for cooling the vehicle interior (AC); and a further operating mode, shown in Fig. 1, in which the scroll compressor is used as part of a battery cooling system in a battery electric vehicle (BATT) or a hybrid electric vehicle (BATT). The individual operating modes differ, in particular, in the control of the displacement machine, with the control specifically relating to the suction pressure.While a low suction pressure, depending on the evaporation temperature between -30° and +20°C, is set in the operating range of a heat pump system (HP), the suction pressure for the operation of a vehicle air conditioning system (AC) is at a medium pressure level, depending on the evaporation temperature between -5° and +30°C. In the operating range for a battery cooling system (BATT), the suction pressure is preferably at the highest level, depending on the evaporation temperature between +10° and +50°C. Another operating mode, not shown in the figures, concerns the operation of the displacement machine as part of a vehicle air conditioning system, wherein the vehicle air conditioning system is mainly used for dehumidifying a vehicle interior (RH), without targeted cooling or heating of the vehicle interior.

[0034] The external lubrication rate increases with increasing speed in all operating modes. The amount of lubricant in the overall system is specifically chosen to be particularly high to ensure the lubrication of the positive displacement machine's components, especially at low speeds. At higher speeds, there is therefore an excess of lubricant in the positive displacement machine, which cannot be retained within the machine and thus enters the overall system (external lubricant circulation rate).

[0035] These varying lubricant circulation rates necessitate a particularly high lubricant quantity in the lubrication system to ensure adequate lubrication of the positive displacement machine's components, especially at low speeds. At low speeds, the positive displacement machine is in a critical lubrication state. Here, exceptionally good lubrication is essential to prevent damage to the machine's components.

[0036] Because of the low lubricant circulation rate at low speeds, the amount of lubricant must be increased to ensure that sufficient lubricant reaches the machine components to be lubricated.

[0037] The invention therefore takes a different approach and instead provides to couple the internal lubricant circulation rate to the rotational speed of the displacement machine.

[0038] This is achieved by a lubricant intermediate storage unit SK, which can be switched from a filling state to a dispensing state by the movement of a movable chamber component of the positive displacement machine. The operation of such a positive displacement machine according to the principle of the invention will be explained in more detail later with reference to Fig. 3.

[0039] The speed-dependent adjustment of the internal lubricant circulation rate can be expected to result in a significantly improved characteristic of the external lubricant circulation rate, as shown schematically in Fig. 2.

[0040] Fig. 2 shows a diagram whose structure is similar to that of the diagram in Fig. 1. Based on calculations of the lubrication system provided in the invention, the corresponding external lubricant circulation rates in the respective speed ranges have now been plotted in the diagram for different operating modes of the positive displacement machine. It can thus be seen that the external lubricant circulation rates are very similar at different speeds in each of the operating modes.

[0041] The speed-dependent adjustment of the internal lubricant circulation rate reduces the increase in the external lubricant circulation rate (OCR) as a function of rotational speed. In most operating modes, it is even possible to achieve a decrease in the external lubricant circulation rate (OCR) with increasing rotational speed. This results in a reduction of the total amount of lubricant in the system. Additionally, the emergency running characteristics of the positive displacement compressor are improved because the speed-adapted internal lubricant delivery allows the internal lubricant supply to be maintained for a longer period. Figures 3a-3c illustrate the operating principle of the invention using an exemplary embodiment. The embodiment shown here relates to a scroll compressor comprising a stationary displacement spiral (FS) and an orbiting displacement spiral (OS).The orbiting displacement spiral OS engages with the stationary displacement spiral FS, forming a volume-variable compression chamber. However, the invention is not only applicable to scroll compressors, but can also be used in reciprocating or rotary compressors.

[0042] For all applications, the positive displacement machine, unlike prior art designs, features a lubricant reservoir SK, which can be integrated into either a movable or a stationary chamber component. The stationary and movable chamber components together form and define a variable-volume compression chamber. In a scroll compressor, as in the example shown in Figures 3a-3c, the stationary chamber component is formed by the stationary displacement spiral FS. The movable chamber component is formed by the orbiting displacement spiral OS.

[0043] In principle, for all types of positive displacement machines, a lubricant separator SA is located downstream of the variable-volume compression chamber in the direction of refrigerant flow. The lubricant contained in the refrigerant, for example, oil, is separated in the lubricant separator SA and preferably directed into a lubricant tank ST of the lubricant separator. From the lubricant separator SA, or from a tank ST of the lubricant separator SA, the lubricant then flows, preferably via a supply line ZL, to the lubricant intermediate storage SK. However, the fluid connection between the supply line ZL and the lubricant intermediate storage SK is not continuous. Rather, the lubricant intermediate storage SK is designed to be filled to a state in which a fluid connection exists between the lubricant intermediate storage SK and the lubricant separator SA.

[0044] In its filled state, the lubricant reservoir SK can therefore be refilled with lubricant from the lubricant separator. The fluid connection to the supply line ZL is open, allowing lubricant to flow from the lubricant tank ST into the lubricant reservoir SK via the supply line ZL. The movement of the movable chamber component, in this case the orbiting displacement spiral OS, closes the fluid connection between the lubricant separator SA and the lubricant reservoir SK at a specific time. In this closed state, the lubricant reservoir SK is not fluidly connected to either the lubricant separator SA or any other components of the displacement machine. The lubricant is thus retained in the lubricant reservoir SK. This state is shown in Fig. 3b. Fig. 3b shows that the displacement spiral OS has been rotated to such an extent that...It was determined that the fluid connection between the supply line ZL and the lubricant reservoir SK has been broken. In this closed state, no further lubricant can be supplied to the lubricant reservoir SK.

[0045] Further rotation of the orbiting displacement spiral OS brings the lubricant reservoir SK into a dispensing state. In this state, a fluid connection exists between the lubricant reservoir SK and the machine components to be lubricated. These components can be, for example, suction-side bearings of the displacement machine. The fluid connection between the lubricant reservoir SK and the machine components to be lubricated can be established via a suitable drain or lubricant dispensing channel. In the dispensing state, the lubricant can be dispensed from the lubricant reservoir SK to the machine components to be lubricated. Since the lubricant reservoir is located in the moving chamber component, namely in the orbiting displacement spiral OS, the filling, holding, and dispensing of the lubricant depend on the rotational speed of the displacement machine.However, it is understood that a similar speed dependency can be achieved if the lubricant intermediate storage SK is not formed in the orbiting displacement spiral, but in the stationary displacement spiral FS.

[0046] The lubricant can be dispensed from the lubricant reservoir, for example, by centrifugal force. Alternatively, the lubricant can be dispensed from the reservoir by gravity and / or flow effects. After the lubricant has been dispensed, the reservoir is emptied, or at least partially emptied, so that it can be refilled with lubricant during the next filling cycle.

[0047] Reference symbol list

[0048] AC vehicle air conditioning mode

[0049] BATT Battery cooling mode FS fixed displacement coil

[0050] HP heat pump mode

[0051] KM Refrigerant

[0052] OCR lubricant circulation rate

[0053] OS orbiting displacement spiral SA lubricant separator

[0054] SK lubricant intermediate storage

[0055] ST lubricant tank

[0056] ZL supply line

Claims

Patent claims 1. Positive displacement machine, in particular a compressor, with at least one volume-variable compression chamber for compressing a refrigerant, which is formed by a stationary chamber component and a movable chamber component, and with a lubrication system for lubricating movable machine components of the positive displacement machine, wherein the lubrication system comprises a lubricant separator (SA) and a lubricant intermediate storage tank (SK) which is arranged downstream of the lubricant separator (SA) in the direction of flow of the lubricant, and wherein the lubricant intermediate storage tank (SK) can be converted from a filling state to a discharge state by the movement of the movable chamber component, wherein the lubricant intermediate storage tank (SK) is fluidly connectable or fluidly connected to the lubricant separator (SA), in particular a lubricant tank (ST) of the lubricant separator (SA), in the filling state, and to the machine components to be lubricated in the discharge state.

2. Displacement machine according to claim 1 characterized in that the lubricant intermediate storage (SK) assumes the filling state and the discharge state at predetermined, independent times, in particular within the working cycles of the compression chamber.

3. Displacement machine according to claim 1 or 2 characterized in that the filling state and the dispensing state are alternately assumed at a frequency that is directly proportional to a rotational speed of the displacement machine.

4. Displacement machine according to one of the preceding claims characterized in that the lubricant intermediate storage (SK) assumes a closed state between the filling state and the dispensing state.

5. Displacement machine according to one of the preceding claims characterized in that the lubricant intermediate storage (SK) is formed in the stationary and / or the movable chamber component.

6. Positive displacement machine according to one of the preceding claims characterized in that the lubricant separator (SA) is arranged downstream of the compression chamber in the direction of flow of the refrigerant.

7. Displacement machine according to one of the preceding claims characterized in that the lubricant intermediate storage (SK) is fluidly connected to the compression chamber and / or to a suction side of the displacement machine and / or to a bearing, in particular a plain bearing or ball bearing, of the displacement machine in the dispensing state.

8. Displacement machine according to one of the preceding claims characterized in that the displacement machine is a scroll compressor, wherein the stationary chamber component is formed by a stationary displacement spiral (FS) and the movable chamber component by an orbiting displacement spiral (OS).

9. Displacement machine according to one of the preceding claims characterized in that the lubrication system is designed without nozzles and / or without throttles.

10. A method for operating a displacement machine, in particular according to one of the preceding claims, comprising the following steps: - Separation of lubricant from a refrigerant-lubricant mixture in a lubricant separator (SA), in particular wherein the lubricant is collected in a lubricant tank (ST) of the lubricant separator (SA); Transfer of the lubricant to a lubricant intermediate storage (LS) while it is in a filling state; Holding the lubricant in the lubricant reservoir (SK) while it is in a closed state; - releasing the lubricant to machine components A positive displacement machine transfers lubricant from the lubricant intermediate storage (SK) while the latter is in a dispensing state; wherein the transfer, holding, and dispensing of the lubricant occur at independent times, and wherein the filling state, closing state, and dispensing state of the lubricant intermediate storage (SK) are produced alternately, in particular independently of time, by a relative movement between a stationary chamber component and a movable chamber component of the positive displacement machine.

11. A method according to claim 10, characterized in that the transfer, holding, and dispensing of the lubricant are dependent on the rotational speed of the positive displacement machine.

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