DE102022206830A1 - Thermoelastic energy conversion device and method for controlling and/or regulating a thermoelastic energy conversion device - Google Patents

Abstract

The present disclosure relates to a thermoelastic energy conversion device (10) for heating and cooling a transmission medium (30), comprising at least one conversion device (11), wherein the at least one conversion device (11) has at least one SMA element (20) in an extension direction (E). ), wherein the at least one SMA element (20) is in thermal contact with the transmission medium (30). The thermoelastic energy conversion device (10) further comprises an application device (12) with a drive (40) in order to load the at least one SMA element (20) with a temperature-dependent force profile and a control device (13) for controlling and/or regulating the application device (12), which controls and/or regulates the conversion device (11) with regard to its loading and unloading. In addition, a method for controlling and/or regulating a thermoelastic energy conversion device is disclosed.

Description

The present disclosure relates to a thermoelastic energy conversion device for heating and cooling a transmission medium, such as a liquid or a gas. The present disclosure further relates to a method for controlling and/or regulating such a thermoelastic energy conversion device.

In known elastocaloric heat cooling machines, an element made of a shape memory alloy (abbreviated: SMA) is cyclically stretched and relaxed and this change in shape creates a phase transformation, which in turn leads to a temperature change, which is used accordingly to generate a heat or Represent refrigeration engine. Analogously, the SMA element is also compressed and relaxed. The phase transition is usually a crystal lattice transformation between a high-temperature phase (austenite) and a low-temperature phase (martensite), so that the phase transition causes a temperature change in the material.

It is desirable to provide a method for operating a thermoelastic energy conversion device which increases the service life of such a thermoelastic energy conversion device.

This object is achieved by the thermoelastic energy conversion device according to claim 1 and the method for controlling and / or regulating the thermoelastic energy conversion device according to claim 4.

Further refinements are specified in the dependent claims.

According to one embodiment, a thermoelastic energy conversion device for heating and cooling a transmission medium comprises a housing for receiving the transmission medium. At least one conversion device is arranged in the housing of the thermoelastic energy conversion device. The at least one conversion device has at least one SMA element in an extension direction, which is thermally coupled to the transmission medium. The thermoelastic energy conversion device further comprises an application device with a drive in order to load the at least one SMA element with a temperature-dependent force curve. The loading device is controlled and/or regulated by a control device in such a way that the loading device controls and/or regulates the conversion device with regard to its loading and unloading.

According to a further embodiment, the control device has a drive. The drive is designed to control the loading device in such a way that the conversion device is controlled depending on the temperature, so that the SMA elements of the conversion device are cyclically loaded and unloaded and thereby heat up or cool down cyclically.

The control device also has a force coupling. With the force coupling, mechanical energy, which is supplied to the application device by the conversion device, is coupled out of the energy conversion device.

According to a further embodiment, the loading device has a carriage that is movable in the housing and is connected to one of the ends of the at least one SMA element. Thus, during a cyclic translational movement of the carriage in the extension direction, a cyclic loading and unloading of the at least one SMA element of the conversion device is achieved. Alternatively, when the at least one SMA element of the converter device is subjected to heat, a cyclic translational movement of the carriage in the extension direction is achieved.

• Es wird mindestens einer der folgenden Systemzustände ermittelt:
  • - Eine Temperatur von mindestens einem Übertragungsmedium der Energiewandlungsvorrichtung
  • - Eine Temperatur von mindestens einem SMA-Element der Energiewandlungsvorrichtung
  • - Einem elektrischen Widerstand des mindestens einen SMA-Elements

According to one embodiment, the method for controlling and/or regulating a thermoelastic energy conversion device has the following steps:

• At least one of the following system states is determined:
  • - A temperature of at least one transmission medium of the energy conversion device
  • - A temperature of at least one SMA element of the energy conversion device
  • - An electrical resistance of the at least one SMA element

Furthermore, a maximum path amplitude that is used in an application device of the energy conversion device is determined. The determined maximum path amplitude depends on the at least one system state.

Based on this, a drive of the loading device is controlled and/or regulated so that the SMA element is stretched by a path length. The path length around which that SMA element is stretched is less than or equal to the maximum path amplitude.

According to one embodiment, the temperature of the at least one transmission medium of the energy conversion device is determined by measuring and/or calculating the temperature of the transmission medium. With a variety of transmission media, either the temperature of a single transmission medium is measured and/or calculated or the temperature of all transmission media is measured and/or calculated.

According to a further embodiment, the temperature of the at least one SMA element of the energy conversion device is determined by measuring and/or calculating the temperature of the SMA element. With a large number of SMA elements, either the temperature of a single SMA element is measured and/or calculated or the temperature of all SMA elements is measured and/or calculated.

According to a further embodiment, the electrical resistance of the at least one SMA element of the energy conversion device is determined by measuring the electrical resistance of the SMA element. With a large number of SMA elements, either the electrical resistance of a single SMA element is measured or the electrical resistance of all SMA elements is measured.

According to a further embodiment, the electrical resistance of the SMA elements is measured in a plurality of SMA elements via a series connection.

According to a further embodiment, the electrical resistance of the SMA elements is measured in a plurality of SMA elements via a parallel connection.

Based on the electrical resistance of the SMA element, conclusions can be drawn about the degree of phase transformation of the SMA element.

Such a method prevents the expansion and compression of the SMA element from being constant and independent of the temperature of the transmission medium or SMA element.

There is a temperature T_D above which the phase transformation can no longer occur through a change in shape. This would lead to problems during operation or even in the idle state if the temperature T_D is exceeded. From this temperature T_D onwards, unwanted plastic deformations of the SMA element can occur, which can firstly be irreversible and secondly can lead to damage to the SMA element, which later leads to failure, such as a break, a crack, etc. leads.

According to a further embodiment, an operating state of the energy conversion device is determined. If the operating state is determined to be switched off, then the application device is activated in such a way that the SMA element of the energy conversion device is relaxed. In this context, switched off means that the drive that drives the application device is, for example, de-energized.

The service life increases due to the additional controllability of the power and efficiency depending on the temperature.

In addition, the method for controlling and/or regulating the thermoelastic energy conversion device offers a protective function in critical temperature ranges.

According to embodiments, the method is designed to control and/or regulate an energy conversion device described here. Features and advantages of the energy conversion device also apply to the process and vice versa.

The invention is explained in more detail below with reference to figures.

• 1 ein Ausführungsbeispiel einer thermoelastischen Energiewandlungsvorrichtung in einer schematischen Ansicht,
• 2 ein Ausführungsbeispiel einer thermoelastischen Energiewandlungsvorrichtung in einer alternativen schematischen Ansicht,
• 3 schematische Darstellungen eines Kreisprozesses zur Wärme- und Kältegenerierung durch einen Phasenübergang anhand eines diskontinuierlichen Prozesses,
• 4 schematische Darstellungen eines Kreisprozesses einer Wärme-Kraft-Kopplung.

Show it:

• 1 an embodiment of a thermoelastic energy conversion device in a schematic view,
• 2 an embodiment of a thermoelastic energy conversion device in an alternative schematic view,
• 3 schematic representations of a cycle for generating heat and cold through a phase transition using a discontinuous process,
• 4 Schematic representations of a cycle process of a heat-power coupling.

Elements of the same construction and function are marked with the same reference numerals across the figures.

1 shows a schematic view of a thermoelastic energy conversion device 10 for heating and cooling a transmission medium 30. The thermoelastic energy conversion device 10 comprises a housing 17 for receiving the transmission medium 30. At least one conversion device 11 is arranged in the housing 17 of the thermoelastic energy conversion device 10. The at least one conversion device 11 has at least one SMA element 20 in an extension direction E, which is thermally coupled to the transmission medium 30.

The thermoelastic energy conversion device 10 further comprises an application device 12 with a drive 40 in order to load the at least one SMA element 20 with a temperature-dependent force curve. The load causes the SMA element 20 to be stretched by a distance L. The path length L is at most as large as the maximum path amplitude W_max.

During operation, the loading device 12 is controlled and/or regulated by a control device 13 in such a way that the loading device 12 controls and/or regulates the conversion device 11 with regard to its loading and unloading.

The control device 13 also has a force coupling, which is realized, for example, by means of the drive 40. With the force coupling, mechanical energy, which is supplied to the application device 12 by the conversion device 11, is coupled out of the energy conversion device 10.

By exerting a tensile force on the SMA elements 20 of the conversion device 11, they heat up, while relieving the load on the conversion device 11 causes heat to be absorbed from the environment. With the help of a drive 40, the carriage 15 is moved back and forth according to a predetermined movement profile. The movement profile is specified, for example, by the maximum path amplitude W_max of the application device 12.

The SMA elements 20 of the conversion device 11 are preferably relaxed in a position of the carriage 15 or are only loaded with a preload that has been set in each case. By moving the carriage 15 in the extension direction E of the SMA elements 20 of the conversion device 11, these are alternately loaded and relieved, in particular stretched and compressed (or relieved). The carriage 15 is preferably displaced in the extension direction E in order to avoid a bending load on the SMA elements 20, which can lead to increased material fatigue.

The thermoelastic energy conversion device 10 can alternatively comprise, for example, two conversion devices 11 (not shown in the figures). Thus, by exerting a tensile force on the SMA elements 20 of one of the conversion devices 11, the SMA elements 20 can heat up, while relieving the SMA elements 20 of the other conversion devices 11 causes heat to be absorbed from the environment.

The device can generally be used for heat and cold generation or for heat-power coupling to convert thermal potential differences into mechanical energy.

The material of the SMA elements 20 can contain a shape memory alloy, such as nickel-titanium, and thus release or absorb latent heat through a phase transition, i.e. a transformation of the lattice structure, during elastic tension or relaxation. Typically, in shape memory alloys that are subjected to mechanical deformation under the influence of force, an austenitic material structure transforms into a martensitic material structure and releases heat in the process. If the material is relieved, it returns to its original shape due to the elastic deformation, with the martensitic material structure changing back into an austenitic material structure and thereby absorbing heat from the environment. Other materials that show a corresponding reversible thermal change in response to an applied mechanical stress field can also be used for the thermoelastic elements.

An embodiment in which the variable path amplitude W_max is used as an example is a spindle that is driven by an electric motor. The rotational movement of the motor is converted into a variable path. The motor is either angle controlled or the spindle stroke is measured and thus a variable stroke of the
Drive set or regulated. The electric drive is expediently configured in such a way that during the relaxation stroke the mechanical energy is recuperated into electrical energy and thus remains in the system.
When driving via a spindle motor system, it is possible to use the drive system simultaneously for loaded and unloaded SMA elements 20, i.e. to couple it mechanically. Alternatively, a separate drive 40 can be used for the loaded part and the unloaded part of the SMA elements 20.

• - Eine Temperatur des mindestens einen Übertragungsmediums 30 der Energiewandlungsvorrichtung 10
• - Eine Temperatur des mindestens einen SMA-Elements 20 der Energiewandlungsvorrichtung 10
• - Einem elektrischen Widerstand des mindestens einen SMA-Elements 20.

In order to optimally use the thermoelastic energy conversion device Method for controlling and / or regulating the thermoelastic energy conversion device 10 with the following steps applied. First, at least one of the following system states is determined:

• - A temperature of the at least one transmission medium 30 of the energy conversion device 10
• - A temperature of the at least one SMA element 20 of the energy conversion device 10
• - An electrical resistance of the at least one SMA element 20.

Furthermore, the maximum path amplitude W_max, which is used in an application device 12 of the energy conversion device 10, is determined. The determined maximum path amplitude W_max depends on the at least one system state. Based on this, the drive 40 of the application device 12 is controlled and/or regulated so that the SMA element 20 is stretched by a path length L.

The path length L by which the SMA element 20 is stretched is less than or equal to the maximum path amplitude W_max.

According to the method for controlling and/or regulating the thermoelastic energy conversion device 10, shape memory alloys whose shape is changed in the superelastic range can be stretched as a function of temperature. i.e. the maximum path amplitude W_max is variable depending on the temperature of the transmission medium 30 and/or the SMA element 20 in order to prevent or at least reduce a critical load. Such a load may result in damage to the SMA element, which later leads to failure such as a break, a crack, or the like.

The temperature of the at least one transmission medium 30 of the energy conversion device 10 is determined by measuring and/or calculating the temperature of the transmission medium 30. With a plurality of transmission media 30, either the temperature of a single transmission medium 30 can be measured and/or calculated or the temperature of all transmission media 30 can be measured and/or calculated. Since the transmission medium 30 is thermally coupled to the SMA element, the temperature of the SMA element can be deduced.

The temperature of the at least one SMA element 20 of the energy conversion device 10 is determined by measuring and/or calculating the temperature of the SMA element 20. With a large number of SMA elements 20, either the temperature of a single SMA element is measured and/or calculated or the temperature of all SMA elements 20 is measured and/or calculated.

The electrical resistance of the at least one SMA element 20 of the energy conversion device 10 is determined by measuring the electrical resistance of the SMA element 20. With a large number of SMA elements 20, either the electrical resistance of a single SMA element 20 is measured or the electrical resistance of all SMA elements 20 is measured. The measurement is measured either via the electrical resistances of the SMA elements 20 connected in series or in parallel.

The measured electrical resistance of the SMA element 20 is a reference variable for the phase transformation of the SMA element 20. Regular repeated resistance measurements of the SMA elements 20 or bundles can be used in conjunction with the then current measured temperature to record changes and wear of the SMA element 20 over a long period of time SMA-Elements 20 can be recognized early, as the resistance changes depending on the relative phase proportions in the material.

Accordingly, the operating strategy can then be adjusted and, for example, the maximum path amplitude can be restricted.

Another aspect is that in the resting state of the thermoelastic energy conversion device 10, the SMA elements 20 are placed in a defined relaxed state. For example, in machine concepts that generate a phase transition by compressing the SMA elements 20, this rest state means that the SMA elements 20 are partially or uncompressed. In machine concepts that generate a phase transition through stretching, this resting state means that the SMA elements 20 are partially or unstretched. This applies analogously to torsion and bending.

For this purpose, an operating state of the thermoelastic energy conversion device 10 is determined. If the operating state is determined to be switched off, then the application device 12 is controlled in such a way that the SMA element 20 of the energy conversion device 10 is relaxed. In this context, switched off means that the drive 40, which drives the application device 12, is, for example, de-energized.

This prevents an SMA element 20, which is in the tensioned state, from becoming close to or above due to a temperature increase T_D is damaged. This can happen, for example, in a motor vehicle due to solar radiation.

Another regulatory and control aspect is the following: if the maximum path amplitude W_max of the SMA element 20 must be restricted and/or thus the
Temperature change due to phase transformation is smaller
If the system fails, the output of the heating/cooling machine automatically drops. This can be partially or fully compensated for by reducing the machine cycle time accordingly. The cycle time is the period of time between stretching and relaxation or compression and relaxation and the associated double phase transformation of the SMA material 20.

2 shows how too 1 a thermoelastic energy conversion device 10 for heating and cooling a transmission medium 30 in an alternative schematic view. A repeated description of the energy conversion device 10 is omitted here.

3 and 4 show an adiabatic cycle for heat and cold generation or an adiabatic cycle for heat-power coupling

In 3 is an adiabatic cycle for the generation of heat and cold through a phase transition of an SMA element 20 in a discontinuous process. Starting from a phase P1 in which the SMA element 20 has a temperature T1, latent heat is released during an adiabatic elastic deformation of the SMA element 20 (the elastic tension ε increases), so that the SMA element 20 rises heated to a temperature T2. In a phase P2, the heat released is dissipated via a heat sink while the deformation remains constant, so that the temperature of the SMA element 20 decreases to a temperature T3. In a phase P3, the SMA element 20 is relaxed again adiabatically (ε decreases) and thereby absorbs latent heat, so that its temperature decreases and after the relaxation process a temperature T4 is reached, as is illustrated in phase P4. By absorbing heat from a heat source, the temperature of the SMA element 20 is increased back to the initial temperature T1 for the phase P1 process.

In 4 an adiabatic cycle for a heat-power coupling is shown through a phase transition of an SMA element 20 in a discontinuous process. Starting from a phase K1, in which the SMA element 20 is heated from a temperature T1 to a temperature T2 in a long configuration, constant expansion ε2, the SMA element 20 is tensioned. In a phase K2, the SMA element 20 transforms from martensite (long) to austenite (short) with a change in elongation ε1 to ε2 and exerts a mechanical force on the loading device 12. In phase K3, the material cools from T2 to T1 in a short configuration ε1 and transforms from austenite to martensite. In K4, the material is drawn out from ε1 to ε2 by the loading device 12 at a constant temperature T1. The force required is significantly lower than is delivered to the loading device 12 in K2.

It makes thermodynamic sense to provide holding phases between the loading and unloading phases that have a constant load curve or a load curve with a gradient that is very small in magnitude and essentially makes no contribution to the generation of heat or cold. In other words, in the holding phases, the load progression should be reduced in such a way that the heat release of heat generated in the previous load phase or the heat absorption of the previous relief phase are effected without additional caloric effects. The holding phase can be correspondingly short if the previous loading and unloading was so slow that the energy from the latent heat is released directly from the medium without any significant delay. This is particularly advantageous for isothermal-adiabatic processes.

The thermoelastic energy conversion device 10 and the method of controlling and/or regulating such a thermoelastic energy conversion device 10 can advantageously be used, among other things, in the automotive sector. The process can minimize negative effects on service life. Temperature changes caused by external influences, such as solar radiation on a parked motor vehicle, can be better taken into account. This prevents the SMA elements 20 from overheating and being damaged above a critical temperature because the SMA element 20 has already carried out a phase transformation and is no longer relaxed. On the other hand, it can be taken into account that below a critical temperature no phase transformation takes place and the device is not ready for operation. This can be counteracted by preheating the device, as is the case with diesel engines, for example.

Reference symbol list

10

Thermoelastic energy conversion device

11

Conversion facility

12

loading device

13

Control device

15

Sleds

17

Housing

20

SMA element

30

transmission medium

40

drive

E

Extension direction

W_max

maximum path amplitude

L

path length

Claims (10)

Thermoelastic energy conversion device (10) for heating and cooling a transmission medium (30), comprising: - at least one conversion device (11), wherein the at least one conversion device (11) has at least one SMA element (20) in an extension direction (E), the at least one SMA element (20) being in thermal contact with the transmission medium (30). contact is established; - an application device (12) with a drive (40) in order to load the at least one SMA element (20) with a temperature-dependent force curve; - a control device (13) for controlling and/or regulating the loading device (12), which controls and/or regulates the conversion device (11) with regard to its loading and unloading. Thermoelastic energy conversion device (10). Claim 1 , wherein the control device (13) has: - a drive (40) which is designed to control the application device (12) in such a way that the conversion device (11) is controlled in a temperature-dependent manner so that the at least one SMA element (20) of the Conversion device (11) is cyclically loaded and unloaded and thereby heats up or cools down cyclically; - A force coupling which is designed to decouple mechanical energy, which is supplied to the application device (12) by the conversion device (11), from the energy conversion device (10). Thermoelastic energy conversion device (10). Claim 1 or 2 , wherein: - the loading device (12) has a movably arranged carriage (15) which is connected to one of the ends of the at least one SMA element (20), - so that during a cyclic translational movement of the carriage (15) in the extension direction (E) a cyclic loading and unloading of the at least one SMA element (20) of the conversion device (11) is achieved, or - so that when the at least one SMA element (20) of the conversion device (11) is subjected to thermal loading, a cyclic translational movement of the carriage (15) in the extension direction (E) is achieved. Method for controlling and/or regulating a thermoelastic energy conversion device (10), the method comprising: - Determine at least one of the system states: - a temperature of at least one transmission medium (30) of the energy conversion device (10), and/or - a temperature of at least one SMA element (20) of the energy conversion device (10), and/or - an electrical resistance of the at least one SMA element (20), - Determining a maximum path amplitude (W_max), which is used in an application device (12) of the thermoelastic energy conversion device (10), depending on the at least one determined system state, - Controlling and/or regulating a drive (40) of the application device (12) so that the SMA element (20) is stretched by a path length (L) in which the path length (L) is less than or equal to the maximum path amplitude (W_max). Procedure according to Claim 4 , in which determining the temperature of the at least one transmission medium (30) comprises: - measuring and/or calculating the temperature of the at least one transmission medium (30). Procedure according to Claim 4 or 5 , in which determining the temperature of the at least one SMA element (20) comprises: - measuring and/or calculating the temperatures of the at least one SMA element (20). Procedure according to one of the Claims 4 until 6 , in which determining the electrical resistance of the at least one SMA element (20) comprises: - measuring the electrical resistance of the at least one SMA element (20). Procedure according to Claim 7 , wherein the device has a plurality of SMA elements (20), in which determining the electrical resistance of the at least one SMA element (20) comprises: - Measuring the electrical resistance of all SMA elements (20) together via a series connection. Procedure according to Claim 7 , wherein the device has a plurality of SMA elements (20), in which determining the electrical resistance of the at least one SMA element (20) comprises: - measuring the electrical resistance of all SMA elements (20) together via a parallel connection. Method according to one of the claims Claim 4 until 9 , comprising: - Determining an operating state, and if the operating state is determined to be switched off: - Controlling the application device (12) so that the SMA element (20) is relaxed.

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