The invention relates to a driveline for a heat exchanger. More specifically, the inven- tion relates to a driveline comprising a motor, a pump and a device arranged to pre- vent overloading and overheating of the motor. Prior art and drawbacks thereof

A heat exchanger comprises a closed circuit in which a working medium circulates through a compressor, a condenser, a choke valve and an evaporator. The compressor is driven by a motor, typically an electric motor. The compressor may be a pump.

The compressor draws in a working medium at a low temperature, generally in the form of a gas, from the evaporator. The evaporator is arranged on the cold side of the system, for example on the outside of a house wall. The evaporator absorbs heat by cooling the surroundings. The condenser gives off heat to the surroundings and is ar- ranged on the warm side of the system, for example in a room in a house.

The compressor forces the working medium in a gaseous state into the condenser. At the end of the condenser, a choke valve is arranged. The choke valve makes the working medium which is forced into the condenser by the compressor be compressed so that the pressure and temperature of the working medium rise. When the pressure rises, the boiling point also increases, so that the working medium goes from a gase- ous state into a liquid state, and the working medium gives off heat into the surround- ings.

When the compressed working medium is forced through the choke valve and into the evaporator, the pressure is reduced so that the working medium which is now in a liquid state evaporates. The working medium is cooled before it is drawn into the compressor and forced into the condenser again. The working medium, also known as a refrigerant, is usually a fluid having the proper- ty of the fluid evaporating and condensing at different temperatures. The working me- dium may, for example, be ammonia, carbon dioxide, hydrocarbons and HCFC gas, for example of the R410A type.

It is known that the energy consumption of a heat exchanger increases in falling tem- peratures. One reason is that the viscosity of the working medium increases so that it will be heavier for the compressor to pump the working medium through the system.

A typical air-to-air heat exchanger for a house takes heat from the outdoor air. To be able to take heat from the outdoor air, the temperature of the evaporator must be lower than that of the outdoor air. In this connection, it is known that cold and moist air may form frost on the evaporator. To remove the frost, the heat exchanger must typically be stopped and reversed so that the frost melts. This process is called de- frosting. Frost formation may occur as early as at 5 degrees Celsius, and the defroster process may typically take 20-30 minutes. It is known that repeated defrosting and high viscosity of the working medium may result in the motor overheating. In addi- tion, the heat exchanger will not produce heat while defrosting, which reduces the overall efficiency of the heat exchanger.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through the features that are specified in the description below and in the claims that follow.

General description of the invention

The invention relates to a driveline for a heat exchanger, the driveline comprising a motor with a motor speed and a pump with a pump speed, the pump being arranged to pump a fluid through a closed circuit belonging to the heat exchanger. The driveline further includes a torque clutch arranged to transmit power from the motor to the pump, the torque clutch being arranged to maintain the motor speed by reduced pump speed.

The heat exchanger may be a heat pump, for example. By a fluid may be understood, herein, a working medium arranged to absorb and give off heat in a closed circuit. By a torque clutch may be understood a torque limiter, an overload clutch or a slipping clutch.

The torque clutch comprises a motor side, also known as a driving side and an input side. The torque clutch includes a pump side, also known as a machine side and an output side.

The torque clutch is arranged to protect machines and components from damage in consequence of overload by the torque clutch being able to equalize different speeds on, respectively, the motor side and pump side. Overload may arise by the torque becoming too great or the speed becoming too high. The torque clutch may be fric tion-based . The torque clutch may be roller- or ball-based. The torque clutch may be a turbine clutch.

The effect of being able to maintain the speed of the motor when the speed of the pump is reduced is a reduction in the risk of overloading, damaging and overheating the motor by increasing and great strain on the pump. Thereby, the wear on the mo- tor can be reduced, which contributes to an increased life time of the motor and lower maintenance costs, compared with those of a motor with an uneven and, at times ex- cessive, load. Further, a constant and optimum speed may contribute to lower power consumption than a motor with varying load and speed.

The speed of the pump is typically reduced in low temperatures because of increased viscosity of the fluid. By arranging a torque clutch between the motor and the pump as described by the invention, the pump may work at a lower speed by lower tem- peratures and increased counterpressure, while, at the same time, the speed of the motor is maintained so that the motor avoids overload.

When the speed of the pump is reduced, the volume flow in the closed circuit is re- duced as well. When the volume flow is reduced, the amount of heat that is transport- ed from the condenser to the evaporator is reduced as well. Less heat gives less dif ference in temperature, and thereby less risk of frost formation on the condenser. Less frost formation gives, in its turn, less need of defrosting . Thereby the heat ex- changer can provide a continuous, but reduced, volume flow.

Even though the reduced volume flow reduces the efficiency of the heat exchanger compared with normal operation, the invention described herein may give a higher efficiency altogether, compared with a prior-art heat exchanger in which the pump will have to be stopped and possibly reversed for defrosting .

The torque transmitted via the torque clutch may be adjusted between a minimum torque and a maximum torque.

By adjusting the torque in the torque clutch, it is possible to adjust at what load the torque clutch is to allow a slippage between the motor side and the pump side in order thus to reduce the torque that is being transmitted. A low torque setting will entail a quick reduction in the pump speed when the counterpressure in the closed circuit in- creases, so that the motor will have a minimal load increase or no load increase. A high torque setting will entail a slow reduction in the pump speed by an increasing counterpressure in the system, which may give increased load on the motor. A person skilled in the art will be able to set the optimum torque with respect to both the motor and the flow in the closed circuit.

The torque clutch may be taken from a group comprising a plate clutch, a centrifugal clutch, a conical clutch, an electromagnetic clutch and a fluid clutch. The torque may set, for example, with an adjusting nut arranged on a driveshaft.

The effect of using a torque clutch as mentioned above is that the driveline can be equipped with a prior-art torque clutch, and with a clutch adapted for a specific instal lation of the driveline. The effect of being able to set the torque with an adjusting nut is that the torque can be set by the use of a simple tool.

The driveline may include a transmission arranged to drive a generator.

The effect of providing the driveline with the transmission is that, in addition to driving the heat pump, the motor can be utilized for driving a generator arranged to charge a battery. The transmission may be connected to the pump side of the driveline so that the clutch also transmits the power that is used for the generator.

The transmission may include a transmission torque clutch.

The effect of the transmission torque clutch is the ability to equalize a possible speed difference between the motor and the generator if the overall load from the pump and the generator becomes too great for the motor. If the overall load becomes too great, a correctly set transmission torque clutch may reduce the torque transmission to the generator, so that the pump may maintain its speed for a longer period on increased resistance in the closed circuit.

If the output of the motor is 2.5 kW, the torque clutch may, for example, be set at 2.5 kW and the transmission clutch at 0.5 kW. As long as the pump does not require more than 2.5 kW, 0.5 kW may be transmitted to the generator. When the pump requires more power, for example 2.3 kW, because of increased flow resistance, the torque transmission through the transmission torque clutch is reduced by 0.3 kW. Thereby the function of the pump may be prioritized over that of the generator, so that the pump may, if necessary, receive all the power available from the motor.

The transmission torque clutch may be connected to the motor side or the pump side.

The transmission torque clutch may be taken from a group comprising a plate clutch, a centrifugal clutch, a conical clutch, an electromagnetic clutch and a fluid clutch. The torque may, for example, be set with an adjusting nut arranged on a driveshaft.

The effect of using a transmission torque clutch as mentioned above is that the driveline may be equipped with a prior-art clutch, and with a clutch adapted for a spe- cific installation of the driveline.

The transmission may have been taken from a group comprising a belt drive and a chain drive.

A belt drive, comprising a V-belt or a toothed belt, for example, has few parts and a low weight compared with a transmission comprising a plurality of gears, chain wheels and/or chains. A belt drive is further known to generate little noise, which is advanta- geous if the transmission is arranged in or near a living room or an outdoor sitting area.

In what follows, examples of preferred embodiments are described, which are visual- ized in the accompanying drawings, in which :

Figure 1 shows a schematic drawing of a driveline according to the invention;

Figure 2 shows a principle drawing of the driveline in section; and Figure 3 shows the driveline of figure 2 on a smaller scale, connected to a genera- tor.

Figure 1 shows a heat exchanger 1 comprising a closed circuit 2 with a pump 30, a condenser 51, a choke valve 50 and an evaporator 52. The pump 30 is driven by a motor 20. The pump 30 is part of a driveline 10 which also includes the motor 20 and a torque clutch 40. In the figure, the torque clutch 40 is shown as an adjustable torque clutch 40 and is arranged between the motor 20 and the pump 30. The torque clutch 40 is arranged to transmit a torque and a speed from the motor 20 to the pump 30.

The condenser 51 is arranged on an inside A and gives off heat. The evaporator 52 is arranged on an outside B and absorbs heat. The motor 20 is adapted for a motor speed of, for example, 100 %. In a normal situa- tion, the pump 30 will have a corresponding pump speed of 100 %. If a counterpres- sure in the closed circuit 2 becomes too great, the speed of the pump 30 may become reduced to less than 100 %. When the pump speed is being reduced to less than 100 %, the torque clutch 40 will slip so that the motor 30 maintains a 100 % motor speed.

Figure 2 shows a principle drawing of the driveline 10 in section. The driveshaft 21 of the motor 20 is provided with a threaded portion 23 at its end portion 22. An torque clutch 40 is arranged at the end portion 22 of the driveshaft 21. The torque clutch 40 includes a motor side 41 attached to the driveshaft 21, and a pump side 42 attached to the pump 30 via an external pump shaft 31.

In the figure, the torque clutch 40 is shown as a conical clutch, in which the pressure between a first conical friction surface 46 belonging to the motor side 41 of the instan- taneous clutch 40 and a second conical friction surface 47 belonging to the pump side 42 of the torque clutch 40 can be adjusted by means of an adjusting nut 44. When the adjusting nut 44 is tightened, a torque spring 43 will be tightened and press the first conical friction surface 46 against the second conical friction surface 47 with the aim of increasing the torque that can be transmitted from the motor 20 to the pump 30.

When the adjusting nut 44 is loosened, the torque spring 43 will relax so that the torque that may be transmitted is reduced. For the adjusting nut 44, a counternut 45 is arranged, adapted for preventing an unintended rotation of the adjusting nut 44.

The motor side 41 of the torque clutch 40 is connected to a seal casing 48 via a threaded connection 49.

Figure 3 shows a principle drawing in section of the driveline 10 connected to a gener- ator 60. A first belt wheel 61 is arranged on the driveshaft 31 of the pump, so that the first belt wheel 61 rotates together with the driveshaft 31. A belt 64 provides for the transmission of a torque and a speed from the first belt wheel 61 to a second belt wheel 62 connected to a generator shaft 63 so that the generator 60 can generate a voltage, for example for charging a battery.

It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative em- bodiments without departing from the scope of the attached claims. In the claims, reference numbers in brackets are not to be regarded as restrictive.

The use of the verb "to comprise" and its different forms does not exclude the pres- ence of elements or steps that are not mentioned in the claims. The indefinite article "a" or "an" before an element does not exclude the presence of several such elements.