EP2989397B1 - Method and device for cooling an engine - Google Patents

Description

The invention relates to a method for cooling an engine according to the preamble of claim 1 and an apparatus for performing the method.

Such a refrigerant circuit with a two-stage compressor is used, for example, in connection with heat pumps. The two compression stages of the compressor are driven by a motor that is mechanically connected to it. With the help of the first compression stage of the compressor, the refrigerant gas is compressed from a low level to a medium level. In the second compression stage, the pressure level is then increased further until the refrigerant has a high pressure level. Heat can then be released from the refrigerant via a condenser connected downstream of the second compression stage, which is then expanded and can again absorb heat in an evaporator in order to be supplied in gaseous form to the first compression stage of the compressor.

Depending on the mode of operation, such a refrigerant circuit can be used to heat or cool a room, for example. The refrigerant also serves to cool the engine, which can be operated at an optimal operating temperature.

In refrigerant circuits, the motor of the compressor is usually cooled either by the coolant drawn in by the compressor or by the gaseous coolant that has already been compressed. The engine waste heat is fed to the gaseous refrigerant either directly before or immediately after compression. At Refrigerant circuits with two-stage compressors, which comprise a first compression stage and a second compression stage, are known to cool the engine with the refrigerant which is at a medium pressure level. This then happens either through the suction gas upstream of the second or second compression stage or through the compressed gas at the first or first compression stage.

As a rule, only gaseous refrigerant is used to cool the engine to prevent dilution of the lubricating oil in the engine for lubrication of the engine mounts. This could lead to insufficient lubrication in the bearings and damage the motor. However, cooling with suction gas before compression in the second compression stage of the compressor by heating the suction gas reduces the efficiency of the refrigerant circuit because it causes a decrease in the density of the suction gas and thus in the mass flow conveyed. Cooling the engine with compressed gas after compression in the first compression stage results in losses and increases the temperature of the compressed gas in the first compression stage. This increases the demands on the temperature resistance of the engine.

To cool an engine of a two-stage compressor, it is known to branch off a partial flow from the main refrigerant flow from the refrigerant circuit after a condenser connected downstream of the second compression stage and to conduct it to a motor cooling system via a type of bypass connection. There is a separate expansion in the bypass line, which, depending on the operating mode, requires one or two expansion valves that require separate control.

The known methods for cooling the engine either result in a reduction in the efficiency of the overall system or are relatively complex and can only be implemented with additional lines and expansion valves, for which a separate regulation is still required.

The invention is based on the object of eliminating the disadvantages of the prior art and, in particular, of specifying a method and a device for cooling an engine in which the waste heat of the engine enters the cooling circuit can be returned without having a negative impact on the efficiency of the overall system. The manufacturing effort and the regulatory effort should be as low as possible and be made with as few components as possible.

According to the invention, this object is achieved by a method with the features of claim 1 and by a device with the features of claim 6. Advantageous refinements can be found in the subclaims.

In a method for cooling at least one engine that drives at least one at least two-stage compressor of a refrigerant circuit, which comprises at least a first compression stage and a second compression stage, wherein a refrigerant is passed through the refrigerant circuit, which in the first compression stage from a low pressure level to a medium pressure level and in the second compression stage from the medium pressure level to a high pressure level and after the second compression stage is released to the medium pressure level with heat, it is provided according to the invention that the engine is cooled with a two-phase refrigerant main flow, which the medium Has pressure level.

The two-phase main refrigerant flow contains both gaseous and liquid refrigerants. Since the main refrigerant flow, i.e. usually the entire refrigerant flow, is used for engine cooling, no additional expansion valves are required. Accordingly, no relevant regulation is required. The waste heat dissipated by the engine has no negative impact on efficiency, since it has no negative impact on either the pressure side or the suction side of the compression stages.

For refrigerant compressors with more than two compression levels, the process is used between two of the compression levels. If there is more than one refrigerant compressor, the method can be used between two refrigerant compressors. It can also do more than one engine be cooled, where appropriate, each engine can be assigned its own refrigerant circuit.

In a preferred development, the main refrigerant flow is separated into a liquid refrigerant part and a gaseous refrigerant part after cooling the engine, the gaseous refrigerant part being fed to the second compression stage and the liquid refrigerant part being fed to the first compression stage of the two-stage compressor. After the engine has been cooled, the two-phase refrigerant main flow is separated into the two phases, the gaseous fraction being further compressed in the second compression stage. In the second compression stage, this enables the gaseous refrigerant to be compressed very efficiently to a high pressure at high temperature. A medium pressure container or can be used, for example, to separate the phases of the refrigerant from the main refrigerant stream, which is a collecting container in which the refrigerant is separated into a gaseous fraction and a liquid fraction.

In this case, the refrigerant is preferably evaporated before the first compression stage with the absorption of heat and condensed after the second compression stage with the emission of heat. For this purpose, for example, after the main refrigerant flow has been separated into the liquid and the gaseous refrigerant part, the liquid refrigerant part is expanded with subsequent evaporation in an evaporator, in which heat can be absorbed, for example, from the environment. As a result, the previously liquid refrigerant part also changes into the gaseous phase and is supplied in gaseous form to the first compression stage of the two-stage compressor, where it is compressed and heated. Following the second compression stage, a condenser can be provided, for example, in which the previously gaseous refrigerant part is condensed and heat is emitted, for example, to the environment. From there, the refrigerant is carried on under high pressure and partially liquefied and finally expanded to the medium pressure level.

In a preferred embodiment, the refrigerant part after the first compression stage with that of the second compression stage Heat emission coming refrigerant part merged before use to cool the engine. This combines the two refrigerant parts so that the entire refrigerant flow is available for cooling the engine.

In an alternative embodiment, it is provided that the refrigerant part is fed directly to the second compression step after the first compression stage, the gaseous middle part after cooling the engine being fed to the second compression stage and being brought together with the refrigerant part coming from the first compression stage, the refrigerant -The main flow-forming refrigerant coming from the second compression stage after heat is used to cool the engine. This results in a relatively simple structure, with the entire refrigerant flow then also being used to cool the engine.

In a device for performing the above-mentioned method, which is designed in particular as a two-stage heat pump, air conditioning device or refrigeration system, the invention provides that it has a motor and a refrigerant circuit in which a two-stage compressor with a first compression stage and a second compression stage is arranged , which can be driven by the engine, an engine cooling system being integrated into the refrigerant circuit in such a way that a main refrigerant flow can flow through it, a phase separation element being arranged in the flow direction behind the engine cooling system, which is connected via a suction gas line for a gaseous refrigerant part with the second compression stage and is connected to the first compression stage of the two-stage refrigerant compressor via a first line for a liquid refrigerant part.

As a result, the entire refrigerant, which is at a medium pressure level, can be used to cool the engine and the waste heat can be returned to the refrigerant circuit. This does not have a negative impact on efficiency, since with the help of the phase separation element after the absorption of the engine's waste heat or after the engine cooling, a separation into a gaseous and a liquid refrigerant part takes place, whereby only the gaseous refrigerant part of the second compression stage is fed and thus further compressed. It can therefore be operated with high efficiency.

An additional bypass connection with additional expansion valves to supply the engine cooling can thus be dispensed with. Rather, the engine cooling is simply flowed through by the main refrigerant flow, which can absorb the corresponding heat. No additional regulation is required. This keeps the manufacturing and control costs low.

In a preferred development, an evaporator and, if appropriate, a throttle element and, if appropriate, further components are arranged in the first line before the first compression stage. This allows the refrigerant part, which has been liquid up to that point, to be expanded and evaporated so that it can be supplied in gaseous form to the first compression stage. The evaporator absorbs heat from an environment, which is thereby cooled. The other components include, for example, filters or the like.

It is particularly preferred that a condenser and optionally a throttle element and optionally further components are arranged in a second line of the refrigerant circuit after the second compression stage. In the condenser, heat can be released from the gaseous refrigerant part to the environment after the second compression stage, as a result of which this refrigerant part is at least partially liquefied. The subsequently arranged throttle element, which can be designed, for example, as a simple throttle or as an expansion valve, then relaxes this refrigerant part, so that it can be used in liquid and / or gaseous form for engine cooling at a medium pressure level. The other components can be designed, for example, as cooling elements for power electronics or the like.

In a preferred embodiment, a mixing device is arranged in the refrigerant circuit before the engine cooling, which is connected to a compressed gas line coming from the first compression stage and the second line. The mixer coming from the first compression stage thus meets Refrigerant part and the refrigerant part coming from the second compression stage and can be routed together from there to the engine cooling. The entire refrigerant flow thus serves to cool the engine.

In an alternative embodiment it is provided that the second line is connected to the engine cooling, a compressed gas line coming from the first compression stage opening into the suction gas line leading to the second compression stage. The gaseous refrigerant part after the phase separation element can be combined with the refrigerant part running from the first to the second compression stage before the second compression stage. Even with this simplified structure, the entire refrigerant flow is led to the engine cooling system and used there to absorb waste heat. However, the refrigerant part coming from the first compression stage is not combined with the refrigerant part coming from the second compression stage directly before the engine cooling, but also only passes through the second compression stage.

Further components can be arranged in a refrigerant line between the engine cooling and the phase separating element. These are, for example, throttle elements and / or additional cooling elements, which are used, for example, to cool elements of power electronics.

The refrigerant compressor preferably has more than two compression stages, the method according to one of claims 1 to 5 being applied between two of the compression stages. A very strong cooling can also be achieved in this way.

In a preferred development, the device has two refrigerant compressors, the method according to one of claims 1 to 5 being used between the refrigerant compressors or between compression stages of the refrigerant compressors, optionally with more than one engine cooling. The device can therefore be used very universally.

• Fig. 1 einen Kältemittelkreislauf mit einem zweistufigen Kompressor einer ersten Ausführungsform und
• Fig. 2 einen Kältemittelkreislauf mit einem zweistufigen Kompressor einer zweiten Ausführungsform.

The invention is described in more detail below on the basis of preferred exemplary embodiments in conjunction with the drawings. Show here:

• Fig. 1 a refrigerant circuit with a two-stage compressor of a first embodiment and
• Fig. 2 a refrigerant circuit with a two-stage compressor of a second embodiment.

In Fig. 1 schematically shows a refrigerant circuit 1 of a heat pump, which has a two-stage compressor 2 with a first compression stage 3 and a second compression stage 4. The two-stage compressor 2 is operated with a motor 5, a mechanical connection between the motor 5 and the compression stages 3, 4 of the two-stage compressor 2 not being shown for reasons of clarity.

With the aid of the compression stages 3, 4 of the two-stage compressor 2, the pressure level of a refrigerant is raised from a first pressure level first to a medium pressure level and then to a high pressure level. A fluid that is liquid under excess pressure and becomes gaseous after pressure relief and heat absorption is used as the refrigerant. The refrigerant is supplied, for example, in gaseous form and at low pressure to the first compression stage 3 of the compressor 2, where it is brought to a medium pressure level, while being heated at the same time.

A gaseous refrigerant portion then reaches the refrigerant circuit via a compressed gas line 6 Figure 1 to a mixing device 7 and is merged there with a refrigerant part coming from the second compression stage 4. This refrigerant part had been supplied to the second compression stage of the compressor 2 in gaseous form and with a medium pressure level and was brought to a high pressure level in the second compression stage 4 while being heated. The gaseous refrigerant part is then fed to a condenser 9 via a second line 8 after the second compression stage 4. There is a release of heat from the refrigerant part to an environment or heat sink 10. The condensed heat medium part, which can have both liquid and gaseous phases, is then expanded with the aid of a throttle element 11, which is designed, for example, as an expansion valve, to the average pressure level with which this coolant part arrives at the mixing device 7 and is brought together with the refrigerant part coming from the first compression stage 3.

The merged refrigerant parts, that is to say the main refrigerant flow, which comprises the entire volume flow, passes from the mixing device 7 to an engine cooling of the engine 5 and absorbs heat from the engine 5 there. The main refrigerant stream is then separated in a phase separation element 12 into the gaseous refrigerant part and the liquid refrigerant part. The gaseous refrigerant part is then again fed to the second compression stage 4.

The liquid refrigerant part is expanded with the aid of a throttle element 13, which in turn can be designed as an expansion valve, and fed to an evaporator 14 at low pressure and low temperature, in which the liquid refrigerant part is converted into a gaseous phase. The evaporator 14 absorbs heat from the environment or from a heat source 15, which is absorbed by the refrigerant part. The throttle element 13 and the evaporator 14 are arranged in a first line 16, which connects the phase separating element 12 to the first compression stage 3 of the two-stage compressor 2. In the first compression stage 3 there is then an increase in the pressure of the refrigerant part evaporated in the evaporator 14, so that it can in turn be fed to the mixing device 7 at a medium pressure level and at an elevated temperature.

Figure 2 shows an alternative preferred embodiment, in which corresponding elements are provided with the same reference numerals. In contrast to the embodiment according to Figure 1 After the first compression stage 3, the refrigerant part is not fed to a mixing device upstream of the engine cooling, but rather directly to the second compression stage 4. Since the gaseous refrigerant part coming from the phase separation element 12 also The second compression stage 4 is supplied, the main refrigerant flow in the second compression stage 4 is brought to the high pressure level and heated. After heat has been given off and condensation in the condenser 9 and subsequent expansion via the throttle element 11, the main refrigerant flow, which has gaseous and liquid constituents, then cools the motor 5 and can absorb heat there. The liquid refrigerant part separated from the main flow of refrigerant by the phase separating element 12 is guided via the first line 16 and is first expanded to a low pressure level with the help of the throttle element 13. Evaporation then takes place in the evaporator 14, so that it is finally supplied in gaseous form to the first compression stage 3 of the compressor 3 and is brought to an intermediate pressure level there with simultaneous heating, in order then to reach the second compression stage 4.

In the method according to the invention or in the devices according to the invention, which is in particular a heat pump arrangement, the motor, which is required to drive the two-stage compressor, is cooled with the aid of the main refrigerant flow, that is to say through the entire refrigerant. An additional bypass connection to branch off some of the refrigerant to cool the engine is not required. Accordingly, there is a simplified structure, in particular by reducing the number of expansion valves required and thus simpler regulation.

The engine's waste heat is returned to the refrigerant circuit without reducing the efficiency of the overall system due to the phase separation that occurs after the waste heat has been absorbed.

The procedure according to the invention can be adapted to a refrigeration cycle with a single-stage compressor with relatively little effort, wherein an intermediate injection and an internal heat exchanger or also an intermediate injection and a phase separation can be used in a phase separation element.

Due to the design of the refrigerant circuit, the refrigerant circuit can be reversed for defrosting and / or for cooling operation, but the phase separation element must always be flowed through in the same direction.

Claims (11)

1. Method for cooling a motor, which at least drives an at least two-stage compressor (2) of a refrigerant circuit (1) which comprises at least one first compression stage (3) and a second compression stage (4), a refrigerant being led through the refrigerant circuit (1), being brought from a low pressure level to a medium pressure level in the first compression stage (3) and from the medium pressure level to a high pressure level in the second compression stage (4) and, following the second compression stage (4), being expanded to the medium pressure level, dissipating heat,
   characterized in that
   the motor (5) is cooled with the entire refrigerant stream which circulates in the refrigerant circuit as a two-phase main refrigerant stream which is at the medium pressure level.
2. Method according to Claim 1, characterized in that after cooling the motor (5), the main refrigerant stream is separated into a liquid refrigerant fraction and a gaseous refrigerant fraction, wherein the gaseous refrigerant fraction is fed to the second compression stage (4) and the liquid refrigerant fraction is fed to the first compression stage (3) of the two-stage compressor (2) .
3. Method according to Claim 1 or 2, characterized in that before the first compression stage (3) the refrigerant is evaporated, picking up heat, and after the second compression stage (4) is condensed, dissipating heat.
4. Method according to one of Claims 1 to 3, characterized in that the refrigerant fraction after the first compression stage (3) is combined with the refrigerant fraction coming from the second compression stage (4) after dissipating heat, before it is used for cooling the motor (5).
5. Method according to one of Claims 1 to 3, characterized in that the refrigerant fraction after the first compression stage (3) is fed directly to the second compression stage (4), wherein the gaseous refrigerant fraction after cooling the motor (5) is fed to the second compression stage (4) and is combined with the refrigerant fraction coming from the first compression stage (3), and the refrigerant forming the main refrigerant stream and coming from the second compression stage (4) is used for cooling the motor (5) after dissipating heat.
6. Device, in particular two-stage heat pump, air conditioning appliance or refrigeration system, for carrying out a method according to Claims 1 to 5, comprising a motor (5) and a refrigerant circuit (1), in which there is arranged a two-stage compressor (2) having a first compression stage (3) and a second compression stage (4), which can be driven by the motor (5),
   characterized in that
   a motor cooling system is incorporated into the refrigerant circuit (1) in such a way that the entire refrigerant stream which circulates in the refrigerant circuit can flow through it as a two-phase main refrigerant stream, wherein, in the flow direction after the motor cooling system, there is arranged a phase separation element (12) which is connected via a suction gas line (17) for a gaseous refrigerant fraction to the second compression stage (4) and via a first line (16) for a liquid refrigerant fraction to the first compression stage (3) of the two-stage refrigerant compressor (2).
7. Device according to Claim 6, characterized in that an evaporator (14) and, if appropriate, a throttling element (13) and, if appropriate, further components, are arranged in the first line (16), before the first compression stage (3).
8. Device according to Claim 6 or 7, characterized in that a condenser (9) and, if appropriate, a throttling element (11) and, if appropriate, further components, are arranged in a second line (8) of the refrigerant circuit (1), after the second compression stage (4).
9. Device according to one of Claims 6 to 8, characterized in that a mixing unit is arranged in the refrigerant circuit (1) before the motor cooling system, being connected to a pressurized gas line (6) coming from the first compression stage (3) and to the second line (8).
10. Device according to one of Claims 6 to 8, characterized in that the second line (8) is connected to the motor cooling system, wherein a pressurized gas line (6) coming from the first compression stage (3) opens into the suction gas line (17) leading to the second compression stage (4) .
11. Device according to one of Claims 6 to 8, characterized in that further components are arranged in a refrigerant line between motor cooling system (5) and phase separation element (12) .

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