Improvements to thermal management system

Abstract

In an aspect, the disclosure is directed to a thermal management system, comprising: a refrigerant circuit including a compressor, a condenser, an expansion valve; and an evaporator, which are arranged to compress, condense, expand, and evaporate a refrigerant. The thermal management system further includes a heater positioned to heat the refrigerant downstream from the expansion valve and upstream from the compressor, a control system including a memory and a processor; and a sensor positioned to transmit signals to the control system that are indicative of a pressure of the refrigerant. The memory contains instructions that are executable by the processor to: turn on the heater and cycle the compressor sufficiently to raise the pressure of the refrigerant to a target pressure that is greater than 1 Bar based on the signals from the sensor.

Description

IMPROVEMENTS TO THERMAL MANAGEMENT SYSTEMCross-Reference to Related Applications[1] This application claims the benefit of, and priority to, U.S. provisional patent application no. 62 / 582,201 filed on September 12, 2023, and U.S. provisional patent application no. 63 / 683,643 filed on August 15, 2024, the entire contents of both of which are incorporated by reference in this application, where permitted.Field of the Invention[2] This disclosure relates generally to the field of thermal management systems for electric vehicles, and more particularly to a coolant-refrigerant heat exchanger and associated thermal management system for use in an electric vehicle.Background of the Invention[3] Thermal management systems in electric vehicles (EVs) are known to employ coolant heaters for the purpose of heating coolant that is ultimately circulated through components of the EV that require heating for performance reasons, such as the vehicle’s main battery pack. Additionally, refrigerant heaters are known in EV’s for serving certain specific purposes. However, each of the existing thermal management systems suffers from certain deficiencies. It is of continued interest to improve the performance and efficiency of EV thermal management systems.Summary of the Disclosure[4] In an aspect, the disclosure is directed to a thermal management system, comprising: a refrigerant circuit including a compressor, a condenser, an expansion valve; and an evaporator, which are arranged to compress, condense, expand, and evaporate a refrigerant; a heater positioned to heat the refrigerant downstream from the expansion valve and upstream from the compressor; a control system including a memory and a processor; and a sensor positioned to transmit signals to the control system that are indicative of a pressure of the refrigerant. The memory contains instructions that are executable by the processor to: turn on the heater and cycle thecompressor sufficiently to raise the pressure of the refrigerant to a target pressure that is greater than 1 Bar based on the signals from the sensor.[5] In another aspect, the disclosure is directed to a method of controlling a heater in a thermal management system of a vehicle, the thermal management system including a refrigerant circuit including a compressor, a condenser, a first branch that includes a first expansion valve and a first evaporator, and a second branch that includes a second expansion valve, and a second evaporator, wherein the second evaporator includes an air inlet and an air outlet in order to carry out heat exchange with ambient air, wherein the first branch and the second branch are fluidically in parallel with one another, wherein the refrigerant circuit is arranged to compress, condense, expand, and evaporate a refrigerant, wherein the heater is positioned to heat a first portion of the refrigerant in the first branch without heating a second portion of the refrigerant in the second branch, wherein the first and second branches end at a common outlet conduit so as to cause mixing of the first portion of the refrigerant and the second portion of the refrigerant. The method comprises: a) operating the compressor to circulate the refrigerant in the refrigerant circuit; b) operating the heater to heat the refrigerant, and operating the second evaporator to carry out heat exchange with ambient air to heat the refrigerant; c) checking if a temperature of the refrigerant at an inlet to the first evaporator is less than an ambient air temperature minus a selected minimum temperature differential; and d) based on step c), reducing power to the secondary heater so as to maintain at least the selected minimum temperature differential between the temperature of the refrigerant at the inlet to the second evaporator and the ambient air temperature.[6] In yet another aspect, the disclosure is directed to a thermal management system, comprising a refrigerant circuit including a compressor, a condenser, an expansion valve; and an evaporator, which are arranged to compress, condense, expand, and evaporate a refrigerant; a heater positioned to heat the refrigerant; a control system including a memory and a processor; and a sensor positioned to transmit signals to the control system that are indicative of a temperature of the refrigerant. The memory contains instructions that are executable by the processor to: turn on the heater and operate the compressor sufficiently to raise the pressure of the refrigerant to at least a target pressure; determine if the temperature of therefrigerant is higher than a selected threshold temperature; and reduce power to the heater as the temperature of the refrigerant increases based on signals from the sensor, and based on whether the temperature of the refrigerant is higher than the selected threshold temperature.[7] In yet another aspect, the disclosure is directed to a method of controlling a compressor in a refrigerant circuit, comprising:[8] determining a maximum allowable temperature for refrigerant at a first selected point in the refrigerant circuit;[9] determining an actual temperature of the refrigerant at the first selected point in the refrigerant circuit;

[0010] determining a first maximum allowable speed for the compressor based on the actual temperature of the refrigerant at the first selected point, and based on the maximum allowable temperature;

[0011] determining a maximum allowable pressure for refrigerant at a second selected point in the refrigerant circuit;

[0012] determining an actual pressure of the refrigerant at the second selected point in the refrigerant circuit;

[0013] determining a second maximum allowable speed for the compressor based on the actual pressure of the refrigerant at the second selected point, and based on the maximum allowable pressure;

[0014] using the lower of the first and second maximum allowable speeds as a final maximum allowable speed;

[0015] determining a target temperature for the refrigerant at a third selected point in the refrigerant circuit;

[0016] determining an actual temperature of the refrigerant at the third selected point in the refrigerant circuit;

[0017] determining a target speed for the compressor based on the actual temperature of the refrigerant at the third selected point, and based on the target temperature;

[0018] determining, at a first point in time that the target speed is lower than the final maximum allowable speed;

[0019] operating the compressor at the target speed at the first point in time;

[0020] determining, at a second point in time that the target speed is higher than the final maximum allowable speed; and

[0021] operating the compressor at the final maximum allowable speed at the second point in time.

[0022] In yet another aspect, the disclosure is directed to a thermal management system of a vehicle, comprising a refrigerant circuit including a compressor, a condenser, an expansion valve, and an evaporator, wherein the refrigerant circuit is arranged to compress, condense, expand, and evaporate a refrigerant; a heater positioned to heat the refrigerant downstream from the expansion valve and upstream from the compressor; and a control system including a memory and a processor. The memory contains instructions that are executable by the processor for:

[0023] determining a maximum allowable temperature for refrigerant at a first selected point in the refrigerant circuit;

[0024] determining an actual temperature of the refrigerant at the first selected point in the refrigerant circuit;

[0025] determining a first maximum allowable speed for the compressor based on the actual temperature of the refrigerant at the first selected point, and based on the maximum allowable temperature;

[0026] determining a maximum allowable pressure for refrigerant at a second selected point in the refrigerant circuit;

[0027] determining an actual pressure of the refrigerant at the second selected point in the refrigerant circuit;

[0028] determining a second maximum allowable speed for the compressor based on the actual pressure of the refrigerant at the second selected point, and based on the maximum allowable pressure;

[0029] using the lower of the first and second maximum allowable speeds as a final maximum allowable speed;

[0030] determining a target temperature for the refrigerant at a third selected point in the refrigerant circuit;

[0031] determining an actual temperature of the refrigerant at the third selected point in the refrigerant circuit;

[0032] determining a target speed for the compressor based on the actual temperature of the refrigerant at the third selected point, and based on the target temperature;

[0033] determining, at a first point in time that the target speed is lower than the final maximum allowable speed;

[0034] operating the compressor at the target speed at the first point in time;

[0035] determining, at a second point in time that the target speed is higher than the final maximum allowable speed; and

[0036] operating the compressor at the final maximum allowable speed at the second point in time.Brief Description of the Drawings

[0037] The foregoing and other aspects of the invention will be better appreciated with reference to the attached drawings, as follows:

[0038] Figure 1 is a schematic view of a basic vehicular thermal management system using refrigerant, and coolant, in accordance with an embodiment of the present disclosure.

[0039] Figure 2 is a graph with curves illustrating the speed of a compressor and the pressure of refrigerant from the thermal management system shown in Figure 1.

[0040] Figure 3 is another graph with curves illustrating the speed of a compressor and the pressure of refrigerant from the thermal management system shown in Figure 1.

[0041] Figure 4 is a graph with a curve illustrating power inputted to a heater in the thermal management system shown in Figure 1.

[0042] Figure 5 is a general pressure-enthalpy chart for a refrigerant.

[0043] Figure 6 is a pressure-enthalpy chart for the refrigerant in the thermal management system shown in Figure 1 , when controlled according to a first control scheme.

[0044] Figure 7 is a pressure-enthalpy chart for the refrigerant in the thermal management system shown in Figure 1 , when controlled according to a second control scheme.

[0045] Figure 8 is an illustration of a control scheme that employs first, second and third control algorithms for setting a speed of a compressor from the thermal management system shown in Figure 1.

[0046] Figure 9 is a flow diagram of a method of operating the compressor using the control scheme shown in Figure 8.

[0047] Figure 10 is an illustration of a control scheme that employs first and second control algorithms for operating a heater from the thermal management system shown in Figure 1 .DETAILED DESCRIPTION OF THE DISCLOSURE

[0048] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the Figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order toprovide a thorough understanding of the embodiment or embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0049] The terms ‘comprising’ and ‘including’ and their various conjugations (e.g. ‘comprises’) will be understood to be inclusive and open-ended, and not exclusive. This means that if an element A includes or comprises an element B, it will be understood that element A could include or comprise other elements in addition to including or comprising element B. The term ‘having’ and its various conjugations are also to be understood as being open-ended in the same way as ‘comprising’ and ‘including’. These terms are not to be interpreted to exclude the presence of other features, steps or components.

[0050] As used herein, the terms “about” and “approximately” are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions.

[0051] Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise: "or" as used throughout is inclusive, as though written "and / or"; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns such that pronouns should not be understood as limiting anything described herein to use, implementation, performance, etc. by a single gender; "exemplary" should be understood as "illustrative" or "exemplifying" and not necessarily as "preferred" over other embodiments. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description. It will also be noted that the use of the term "a" or "an" will be understood to denote "at least one" inall instances unless explicitly stated otherwise or unless it would be understood to be obvious that it must mean "one".

[0052] Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

[0053] As used in this document, "attached" in describing the relationship between two connected parts includes the case in which the two connected parts are "directly attached" with the two connected parts being in contact with each other, and the case in which the connected parts are "indirectly attached" and not in contact with each other, but connected by one or more intervening other part(s) between.

[0054] As used in this document, terms describing relative positions of elements such as ‘top’, ‘upper’, ‘bottom’, ‘lower’, or other analogous terms will be understood to refer to the placement of the described element during use of the apparatus of which it is a part unless the context would make it clear that it is otherwise. It will be understood that the aforementioned placement of an element, for example, can still be considered its placement even when the object that it is a part of is lying in some position other than the position in which it will be used. As an example, if reference is made to a device having an upper member, it will be understood that the upper member is being described as having an upper position when the device that it is a part of is in use or is in position for use, unless the context would make it clear that it is otherwise. Further to this example, it will be understood that the aforementioned upper member of the object can still be considered its upper member even when the object is lying on its side, for storage, or for transport, or for some other reason.

[0055] "Memory" refers to a non-transitory tangible computer-readable medium for storing information (e.g., data or data structures) in a format readable by a processor, and / or instructions (e.g., computer code or software programs or modules) that arereadable and executable by a processor to implement an algorithm. The term "memory" includes a single device or a plurality of physically discrete, operatively connected devices despite use of the term in the singular. Non-limiting types of memory include solid-state semiconductor, optical, magnetic, and magneto-optical computer readable media. Examples of memory technologies include optical discs such as compact discs (CD-ROMs) and digital versatile discs (DVDs), magnetic media such as floppy disks, magnetic tapes or cassettes, and solid state semiconductor random access memory (RAM) devices, read-only memory (ROM) devices, electrically erasable programmable read-only memory (EEPROM) devices, flash memory devices, memory chips and combinations of the foregoing. Memory may be non-volatile or volatile. Memory may be physically attached to a processor, or remote from a processor. Memory may be removable or non-removable from a system including a processor. Memory may be operatively connected to a processor in such as way as to be accessible by a processor. Instructions stored by a memory may be based on a plurality of programming and / or markup languages known in the art, with non-limiting examples including the C, C++, C#, Python ™, MATLAB ™, Java ™, JavaScript ™, Perl ™, PHP ™, SQL ™, Visual Basic ™, Hypertext Markup Language (HTML), Extensible Markup Language (XML), and combinations of the foregoing. Instructions stored by a memory may also be implemented by configuration settings for a fixed-function device, gate array or programmable logic device.

[0056] Processor" refers to one or more electronic hardware devices that is / are capable of reading and executing instructions stored on a memory to perform operations on data, which may be stored on a memory or provided in a data signal. The term "processor" includes a single device or a plurality of physically discrete, operatively connected devices despite use of the term in the singular. The plurality of processors may be arrayed or distributed. Non-limiting examples of processors include integrated circuit semiconductor devices and / or processing circuit devices referred to as computers, servers or terminals having single or multi-processor architectures, microprocessors, microcontrollers, microcontroller units (MCU), central processing units (CPU), field-programmable gate arrays (FPGA), application specific circuits (ASIC), digital signal processors, and combinations of the foregoing.

[0057] Any method, application or module herein described may be implemented using computer readable / executable instructions that may be stored or otherwise held by a memory, and executed by a processor. Aspects of the present disclosure may be described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor, such that the processor, and a memory storing the instructions, which execute via the processor, collectively constitute a machine for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0058] The flowcharts and functional block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustration, and combinations of blocks in the block diagrams and / or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

[0059] The embodiments of the disclosures described herein are exemplary (e.g., in terms of materials, shapes, dimensions, and constructional details) and do not limit by the claims appended hereto and any amendments made thereto. Persons skilled in the art will appreciate that there are yet more alternative implementations and modifications possible, and that the following examples are only illustrations of one ormore implementations. The scope of the disclosure, therefore, is only to be limited by the claims appended hereto and any amendments made thereto.

[0060] DESCRIPTION OF THERMAL MANAGEMENT SYSTEM

[0061] Reference is made to Figure 1 , which shows a schematic diagram of a thermal management system 10 for a vehicle (not shown), in accordance with an embodiment of the present disclosure. It will be noted that the thermal management system 10 shown in Figure 1 is simplified in the sense that several components that are typically present, have been omitted here for simplicity.

[0062] The vehicle may be an electric vehicle, and may include a passenger cabin, a main battery pack, and a traction motor for driving one or more of the wheels. The electric vehicle may be any type of vehicle that employs a traction motor and a traction battery for supplying power to the traction motor, such as an SUV, an automobile, a light-duty truck, a heavy-duty truck, an off-road vehicle, a vehicle used in construction, an aircraft, or any other suitable type of vehicle. Furthermore, the electric vehicle may contain only a traction motor (or several of them) for driving movement of the electric vehicle, or alternatively, it may contain an internal combustion engine, such as a range extender engine to assist in recharging the main battery pack when the traction battery at or near depletion. In yet other embodiments, the electric vehicle may be a fuel-cell vehicle, generating electric power via a fuel cell, for powering the traction motor.

[0063] The thermal management system 10 includes a refrigerant circuit 12 and a coolant circuit 14. The refrigerant circuit 12 includes a compressor 16, a condenser 18, an expansion valve 20; and an evaporator 22, which are arranged to compress, condense, expand, and evaporate a refrigerant, respectively. The compressor 16, the condenser 18, and the expansion valve 20 may be any suitable compressor, condenser and expansion valve, respectively. The coolant circuit 14 includes a pump 24, and a radiator 26.

[0064] The evaporator 22 may be any suitable evaporator. In the embodiment shown, the evaporator 22 may be a refrigerant / coolant heat exchanger 23, that includes a coolant flow path 26 for transporting coolant therethrough, a refrigerant flow path 28 for transporting refrigerant therethrough. The coolant flow path 26 and the refrigerant flow path 28 are positioned in order to transfer heat from one of the coolantand the refrigerant to the other of the coolant and the refrigerant. The refrigerant / coolant heat exchanger 24 may be as shown and described in PCT patent publication W02023 / 060352 A1 , the contents of which are incorporated herein by reference in their entirety.

[0065] The refrigerant circuit 12 may further include a heater 30 that is positioned to heat the refrigerant downstream from the expansion valve 20 and upstream from the compressor 16. The heater 30 is provided to heat the refrigerant in situations in which it is advantageous to do so. In some cases, the heater 30 may be operated to heat the refrigerant to ensure that the refrigerant is entirely in gas form when entering the compressor 16. In some cases, the heater 30 may be operated to accelerate the increase in pressure in the refrigerant in the refrigerant circuit 12 in situations where the pressure of the refrigerant in at least one area of the refrigerant circuit 12 is below 1 Bar, which increases the risk of leakage of air and contaminants into the refrigerant circuit 12 from outside of the refrigerant circuit 12.

[0066] The heater 30 may be positioned anywhere suitable in the refrigerant circuit 12 for heating the refrigerant. In the embodiment shown, the heater 30 is mounted to the coolant-refrigerant heat exchanger 24 and is positioned to heat both the refrigerant and the coolant in the coolant-refrigerant heat exchanger 24.

[0067] The thermal management system 10 may further include a control system 32, including a memory 32a and a processor 32b. The control system 32 may be configured to control the operation of the compressor 16, the pump 24, the heater 30 and other components of the thermal management system 10. Lines showing connections between the control system 32 and the components controlled by it are not shown so as not to make Figure 1 difficult to understand. The thermal management system 10 may further include a sensor 34 positioned to transmit signals to the control system 32 that are indicative of a pressure of the refrigerant, and in particular, indicative of a pressure of the refrigerant at the inlet to the compressor 16. The inlet to the compressor 16 may be referred to as the compressor inlet 36, and is identified schematically in Figure 1. The compressor 16 also has a compressor outlet shown at 37. It is at the compressor inlet 36 that the pressure of the refrigerant may be lowest in the refrigerant circuit 12. When the vehicle is in an environment that is very cold, the refrigerant in the refrigerant circuit 12 is correspondingly cold, whichreduces its pressure. When the vehicle is started in such an environment, it is advantageous to provide a way of increasing the pressure of the refrigerant quickly and efficiently, to a pressure where there is no longer a risk of leakage inward into the refrigerant circuit 12. In some embodiments, the memory 32a of the control system 32 contains instructions that are executable by the processor 32b to turn on the heater 30 and cycle the compressor 16 sufficiently to raise the pressure of the refrigerant to a target pressure that is greater than 1 Bar based on the signals from the sensor 34.

[0068] Figure 2 is a graph showing the pressure of the refrigerant at the compressor inlet 36 (as illustrated by the curve 38), and the RPM of the compressor 16 (as illustrated by the curve 39). As can be seen, the compressor 16 may be driven initially at a first RPM, which may be 40% of its maximum allowable speed for a first period of time T1 , then is stopped for a second period of time T2, then is driven at a second RPM, which may be 20% of its maximum allowable speed for a third period of time T3, and then is stopped for a fourth period of time T4. The compressor 16 may be further driven at a third RPM, which may be 20% of its maximum allowable speed, for a fifth period of time T5, and then is stopped for a sixth period of time. The compressor 16 may continue to be cycled between a selected RPM and being stopped in order to bring the refrigerant up to a target positive pressure (i.e. , that is greater than 1 Bar). In an example, the target positive pressure may be any suitable pressure, such as 5 psig. Alternatively, a greater or lower target positive pressure may be used.

[0069] Figure 3 shows a first curve 40 which illustrates the RPM of the compressor 16 with respect to time, and a second curve 42, which illustrates the pressure at the compressor inlet 36 with respect to time. Figure 4 shows a curve 44, which illustrates the amount of power being applied to the heater 30. It can be seen that, the power to the heater 30 may in some embodiments, be increased over time, and then, once the control system 32 determines that the pressure at the compressor inlet 36 has increased beyond 1 Bar, the control system 32 may decrease the power to the heater 30, until such time that the control system 32 determines that the pressure at the compressor inlet 36 has increased beyond the target positive pressure. At that point, the control system 32 may switch from driving the compressor 16 in a ‘cold-start’ mode, to driving the compressor in a ‘normal’ mode, in which the compressor 16 is driven to reach a selected operating pressure. In the ‘normal’ mode, the power to the heater 30may be adjusted as is advantageous based on the pressure that is desired, which may itself be based on whatever heat exchange demands there may be.

[0070] The sensor 34 may be any suitable type of sensor. For example, the sensor 34 may be a pressure sensor that is positioned at the compressor inlet 36. Alternatively, the sensor 34 may be a pressure sensor positioned at another location in the refrigerant circuit 12, and appropriate calculations can be performed to determine the pressure at the compressor inlet 36 based on the pressure measured by the sensor 34. The sensor 34 may alternatively be a temperature sensor, positioned at the compressor inlet 36 or elsewhere in the refrigerant circuit 12, and appropriate calculations can be performed to determine the pressure at the compressor inlet 36 based on the pressure measured by the sensor 34.

[0071] Based on the above considerations, the memory 32b of the control system 32 may contain instructions that are executable by the processor 32a to: turn on the heater 30 and cycle the compressor 16 sufficiently to raise the pressure of the refrigerant to a target pressure that is greater than 1 Bar based on signals from the sensor 34 being indicative that the pressure of the refrigerant (at the compressor inlet 36) is less than 1 Bar. The target pressure may be any suitable target pressure, such as about 5 psig.

[0072] DESCRIPTION OF BASIC PRESSURE-ENTHALPY CHART

[0073] Figure 5 is a pressure-enthalpy chart that illustrates the refrigeration cycle that the refrigerant undergoes, in a graphical format. As will be understood by one skilled in the art, the inverted U-shaped line represents the gas / liquid transition properties for the refrigerant. The curve shown at 50 represents the changes in the properties of the refrigerant as it passes through the refrigeration circuit shown in Figure 1. Point 52 represents the properties of the refrigerant immediately upstream of the compressor 16. Curve segment 50a is representative of the change in the properties of the refrigerant due to operation of the compressor 16. Point 54 is representative of the properties of the refrigerant downstream of the compressor 16 and upstream from the condenser 18. As can be seen, the pressure and the temperature of the refrigerant increase between point 52 and point 54.

[0074] Curve segment 50b is representative of the change in the properties of the refrigerant due to operation of the condenser 18. Point 56 is representative of the properties of the refrigerant immediately downstream of the condenser 18 (and therefore upstream from the expansion valve 20). As can be seen, the temperature of the refrigerant decreases and then remains constant during the phase change that occurs in the condenser 18.

[0075] Curve segment 50c is representative of the change in the properties of the refrigerant due to the expansion valve 20. Point 58 is representative of the properties of the refrigerant immediately downstream of the expansion valve 20 and therefore upstream from the evaporator 22). As can be seen, the pressure and temperature of the refrigerant decrease as a result of passing through the expansion valve.

[0076] Curve segment 50d is representative of the change in the properties of the refrigerant due to passage through the evaporator 22. After passing through the evaporator 22, the refrigerant returns to point 52, which is representative of the properties of the refrigerant immediately downstream of the evaporator 22 (and therefore of the properties of the refrigerant immediately upstream of the compressor 16). As can be seen, the pressure and the temperature remain substantially constant in the evaporator 22. This is because the heat being transferred to the refrigerant is being used to drive the phase change (i.e. the evaporation) of the refrigerant, which occurs at a constant temperature, as will be understood by one skilled in the art. Optionally, the evaporator 22 may be sized to transfer to the refrigerant a bit more than the minimum amount of heat that is needed to evaporate all of the refrigerant, so as to drive an increase in temperature of the refrigerant once all of it has evaporated. This ensures that all of the refrigerant leaves the evaporator 22 as a gas, with no fraction thereof remaining as a liquid. It is advantageous for all of the refrigerant to be in gaseous form when reaching the inlet of the compressor 14 so as to avoid damaging the compressor 16.

[0077] DESCRIPTION OF CONTROL OF REFRIGERANT SYSTEM

[0078] Reference is made to Figure 6, which shows a pressure-enthalpy chart. Initially, when the vehicle is immersed in a low temperature environment, the pressure at the compressor inlet 36 (Figure 1) may be less than 1 Bar. The pressure-enthalpycurve for this state is shown at 60. After some time cycling the compressor 16 as described above, the pressure-enthalpy curve for the refrigerant circuit 12 may be as shown at 62 such that the pressure at the compressor inlet 36 is greater than 1 Bar. At a suitable time, the compressor 16 may be operated in a continuous mode where it is not being cycled, so as to bring the pressure at the compressor inlet 36 and at the compressor outlet 37 up towards a desired operating range. The pressure-enthalpy curve for the refrigerant circuit 12 during this progressive state may be as shown at 64. After a further amount of time, the compressor 16 may be operated in a steadystate mode in which the pressure at the compressor inlet 36 and the pressure at the compressor outlet 37 are as desired for the refrigerant circuit 12. The pressureenthalpy curve for the refrigerant circuit 12 during this progressive state may be as shown at 66.

[0079] It will be noted that it is relatively more efficient for the compressor to have a selected pressure differential between the compressor inlet 36 and the compressor outlet 37. A relatively smaller pressure differential between the compressor inlet 36 and the compressor outlet 37 means that the compressor 16 will be operated at a slower speed in order to raise the pressure from the pressure at the compressor inlet 16 to reach the desired pressure at the compressor outlet 37. A relatively greater pressure differential between the compressor inlet 36 and the compressor outlet 37 means that the compressor 16 will be operated at a relatively higher speed in order to raise the pressure from the pressure at the compressor inlet 16 to reach the desired pressure at the compressor outlet 37. In general, when compressors are operated at a lower speed, they are relatively less efficient mechanically. It is therefore desirable from an energy efficiency perspective, to operate a compressor at or near its designed optimum operating speed. The pressure-enthalpy curve shown at 68 in Figure 7 is illustrative of the compressor 16 operating with a low pressure differential between the compressor inlet 36 and the compressor outlet 37. By contrast, the pressure enthalpy curve 66 in Figure 6 is illustrative of the compressor 16 operating with a relatively higher pressure differential between the compressor inlet 36 and the compressor outlet 37. The speed of the compressor 16 operating along the curve 66 is higher (and closer to its optimum speed for peak mechanical efficiency) than the speed of the compressor 16 operating along the curve 68 in Figure 7.

[0080] Separately, it will be noted that the temperature of the refrigerant in the refrigerant circuit 12 is directly proportional to its pressure. Accordingly, as more heat is transferred to the refrigerant, (e.g. from the heater 30), the pressure of the refrigerant increases at the compressor inlet 36.

[0081] While it is desirable to it has been found that it is desirable to increase the pressure of the refrigerant at the compressor inlet 36 to be greater than 1 Bar, it is also desirable to operate the compressor 16 at relatively higher speeds for relatively greater efficiency. In order to meet these parameters, the heater 30 may be controlled in a manner such that, once the control system 32 determines that the temperature of the refrigerant at a selected point in the refrigerant circuit 12 is greater than a selected threshold temperature, the output of the heater 30 may be reduced. The amount of reduction in the output heater 30 may be proportional (linearly or non-linearly proportional) to the temperature of the refrigerant at the selected point in the refrigerant circuit 12 once the temperature of the refrigerant is beyond the selected threshold temperature. The selected threshold temperature may be any suitable temperature such as, for example, 0 degrees Celsius at the inlet to the evaporator 22. To determine the temperature of the refrigerant, the control system 32 may receive signals from a temperature-related sensor (shown at 59 in Figure 1 ), which may optionally be positioned at the inlet of the evaporator 22. The temperature-related sensor 59 may be any suitable type of sensor, such as a temperature sensor. Instead of using a temperature sensor, the temperature-related sensor 59 may be any other type of sensor that permits the determination of the temperature of the refrigerant at the inlet to the evaporator 22. For example, the temperature-related sensor 59 may be a pressure sensor positioned at the inlet to the evaporator 22, or at another location in the refrigerant circuit 12 such as the compressor inlet 36, or the outlet of the evaporator 22. Appropriate calculations can be performed to determine the temperature at the evaporator inlet based on the pressure measured by the sensor 59, and thus the sensor 59 even in embodiments in which it is a pressure sensor, may be referred to as a temperature-related sensor 59. It is possible that the sensor 59 may be the same sensor as the sensor 34.

[0082] Based on the above considerations, the memory 32b may contain instructions that are executable by the processor to: operate the heater 30 at a selected outputpower until the temperature of the refrigerant is higher than a selected threshold temperature, and to reduce power to the heater as the temperature of the refrigerant increases, once the temperature of the refrigerant is higher than the selected threshold temperature. In particular, the memory 32b may further contain instructions that are executable by the processor to: reduce power to the heater 30 as the temperature of the refrigerant (at the compressor inlet 36) increases beyond a selected threshold temperature, such as, for example 0 degrees Celsius. It will be noted that the particular temperature that is the selected threshold temperature depends on certain parameters such as the target output pressure for the compressor 16, and the particular construction of the compressor 16, among other things. The pressureenthalpy curves shown 60, 62, 64 and 66 in Figure 6 are illustrative of the control system 32 being operated according to this control scheme where the power to the heater 30 is reduced as the pressure of the refrigerant increases, thereby operating the compressor 16 at relatively high speed and high mechanical efficiency, and by applying a relatively small amount of power to the heater 30. By contrast, the pressure-enthalpy curves shown 70, 72, 74, and 68 in Figure 7 are illustrative of the control system 32 being operated according to a control scheme where the power to the heater 30 is not reduced as the pressure of the refrigerant increases. As can be seen, and as noted above, when operating along the curve 68 (as compared to operating along the curve 66) the compressor 16 ends up operating with a relatively narrow pressure differential between the compressor inlet 36 and the compressor outlet 37, and thus operates at relatively low speed and correspondingly low mechanical efficiency, while the heater 30 draws a relatively higher amount of power.

[0083] Optionally, when cycling the compressor 16 on and off in order to increase the pressure of the refrigerant at the compressor inlet 36 to the target pressure, the heater 30 may also be cycled, such that the heater 30 may be turned off when the compressor 16 is turned off so as not to impart too much heat to the small portion of the refrigerant in the immediate presence of the heater 30, and so as not to heat the heater 30 beyond its maximum allowable surface temperature in embodiments where the maximum allowable surface temperature is a limiting parameter of the operation of the heater 30.

[0084] Reference is made to Figure 1. As can be seen, optionally, the evaporator 22 and the expansion valve 20 may be a first evaporator 22 and a first expansion valve 20, which are included in a first branch 80 of the refrigerant circuit 12, and the thermal management system 10 may include a second branch 82 that includes a second evaporator 84 and a second expansion valve 86. The second evaporator 84 includes an air inlet and an air outlet in order to carry out heat exchange with ambient air. The first branch 80 and the second branch 82 are fluid ically in parallel with one another, in the sense that the flow of refrigerant in the refrigerant circuit 10 splits such that a first portion of the refrigerant passes through the first branch 80 and a second portion of the refrigerant passes through the second branch 82. The first and second branches 80 and 82 end at a common outlet conduit 88 so as to cause mixing of the first portion of the refrigerant and the second portion of the refrigerant. Optionally, one or more valves are provided (not shown) in order to selectively control refrigerant flow through the first branch 80 and / or through the second branch 82. The valves may be controlled to permit no flow through the first evaporator 80 and flow only through the second evaporator 84, to permit no flow through the second evaporator 84 and flow only through the first evaporator 80, or to permit some flow through both the first and second evaporators 22 and 84.

[0085] As can be seen, the heater 30 is positioned to heat the first portion of the refrigerant in the first branch 80 without heating the second portion of the refrigerant in the second branch 82. The second portion of the refrigerant is heated afterwards once the first and second portions of the refrigerant are mixed together in the common conduit 88.

[0086] The memory 32b of the control system 32 may include instructions that are executable by the processor 32a for:

[0087] a) operating the compressor 16 to circulate the refrigerant in the refrigerant circuit 12;

[0088] b) operating the heater 30 to heat the refrigerant, and operating the second evaporator 84 to carry out heat exchange with ambient air to heat the refrigerant;

[0089] c) checking if a temperature of the refrigerant at an inlet to the first evaporator is less than an ambient air temperature minus a selected minimum temperature differential; and

[0090] d) based on the checking, reducing power to the heater 30 so as to maintain at least the selected minimum temperature differential between the temperature of the refrigerant at an inlet to the second evaporator 30 and the ambient air temperature.

[0091] By maintaining at least the selected temperature differential between the temperature of the refrigerant at an inlet to the second evaporator 30 and the ambient air temperature, the second evaporator 84 can continue to be used to capture ‘free’ heat from the ambient air, thereby improving the power efficiency of the thermal management system 10.

[0092] The selected temperature differential may be any suitable value, such as, for example, 5 degrees Celsius.

[0093] Reference is made to Figure 8, which shows a control scheme for the compressor 16 that can be carried out by the control system 32. In a broad sense, the control system 32 may use a first control algorithm (illustrated at 90) to determine a first maximum allowable speed for the compressor, based on a maximum allowable temperature for the refrigerant. The control system 32 may use a second control algorithm (illustrated at 92) to determine a second maximum allowable speed for the compressor, based on a maximum allowable pressure for the refrigerant. The control system 32 may then use the lower of the first and second maximum allowable speeds as a final maximum allowable speed. The final maximum allowable speed may then be used by the control system in a third control algorithm 94. In the third control algorithm 94, the control system 32 may determine a target speed for the compressor. The control system 32 may check if the target speed is greater than the final maximum allowable speed. If it is less than the final maximum allowable speed, the control system 32 may operate the compressor 16 at the target speed. If it is more than the final maximum allowable speed, the control system 32 may operate the compressor 16 at the final maximum allowable speed. Put another way, the memory 32b may contain instructions that are executable by the processor for:

[0094] determining a maximum allowable temperature for refrigerant at a first selected point in the refrigerant circuit;

[0095] determining an actual temperature of the refrigerant at the first selected point in the refrigerant circuit;

[0096] determining a first maximum allowable speed for the compressor based on the actual temperature of the refrigerant at the first selected point, and based on the maximum allowable temperature;

[0097] determining a maximum allowable pressure for refrigerant at a second selected point in the refrigerant circuit;

[0098] determining an actual pressure of the refrigerant at the second selected point in the refrigerant circuit;

[0099] determining a second maximum allowable speed for the compressor based on the actual pressure of the refrigerant at the second selected point, and based on the maximum allowable pressure;

[0100] using the lower of the first and second maximum allowable speeds as a final maximum allowable speed;

[0101] determining a target temperature for the refrigerant at a third selected point in the refrigerant circuit;

[0102] determining an actual temperature of the refrigerant at the third selected point in the refrigerant circuit;

[0103] determining a target speed for the compressor based on the actual temperature of the refrigerant at the third selected point, and based on the target temperature;

[0104] determining, at a first point in time that the target speed is lower than the final maximum allowable speed;

[0105] operating the compressor at the target speed at the first point in time;

[0106] determining, at a second point in time that the target speed is higher than the final maximum allowable speed; and

[0107] operating the compressor at the final maximum allowable speed at the second point in time.

[0108] The first, second and third control algorithms 90, 92 and 94 may each be a PID control algorithm, or any other suitable type of control algorithm.

[0109] Put another way, the control system 32 may be programmed to carry out a method, illustrated in Figure 9, wherein the aforementioned actions are carried out at steps 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126 and 128, respectively.

[0110] Optionally, the first selected point, the second selected point and the third selected point are all downstream from the compressor 16 and upstream from the condenser 18 (e.g. at the compressor outlet 37).

[0111] As noted above, using different wording, it will be noted that the determining of the first maximum allowable speed may be carried out using a first PID control algorithm. In other words, the first control algorithm 90 may be a first PID control algorithm. Similarly, determining of the second maximum allowable speed may be carried out using a second PID control algorithm. In other words, the second control algorithm 90 may be a second PID control algorithm. Similarly, determining of the target speed may be carried out using a third PID control algorithm. In other words, the third control algorithm 90 may be a third PID control algorithm.

[0112] Reference is made to Figure 10, which shows a control scheme for the heater 30 that can be carried out by the control system 32. In a broad sense, the control system 32 may use a first control algorithm (illustrated at 130) to determine a maximum allowable target temperature for the heater 30, based on a target pressure for the refrigerant at the compressor inlet 36 and an actual pressure for the refrigerant at the compressor inlet 36. The control system 32 may use a second control algorithm (illustrated at 132) to determine a power input for the heater 30, based on the maximum allowable target temperature for the heater 30 and the actual temperature of the heater 30. The control system 32 may then operate the heater 30 at thedetermined power input. Put another way, the memory 32b may contain instructions that are executable by the processor for:

[0113] The refrigerant circuit 12 and the coolant circuit 14 may be used to control the temperature of one or more thermal loads for the thermal management system 10. The thermal loads may include the vehicle’s passenger cabin, the main battery pack for the vehicle, and the power electronics for the traction motor for the vehicle. The vehicle passenger cabin may be considered to be a thermal load to be temperature- controlled using the refrigerant.

[0114] Those skilled in the art will appreciate that the embodiments disclosed herein can be modified or adapted in various other ways whilst still keeping within the scope of the appended claims.

Claims

Claims1 . A thermal management system, comprising: a refrigerant circuit including a compressor, a condenser, an expansion valve; and an evaporator, which are arranged to compress, condense, expand, and evaporate a refrigerant; a heater positioned to heat the refrigerant downstream from the expansion valve and upstream from the compressor; a control system including a memory and a processor; and a sensor positioned to transmit signals to the control system that are indicative of a pressure of the refrigerant, wherein the memory contains instructions that are executable by the processor to: turn on the heater and cycle the compressor sufficiently to raise the pressure of the refrigerant to a target pressure that is greater than 1 Bar based on the signals from the sensor.

2. The thermal management system as claimed in claim 1 , wherein the sensor is a temperature sensor.

3. The thermal management system as claimed in claim 1 , wherein the instructions that are executable by the processor to: turn on the heater and cycle the compressor sufficiently to raise the pressure of the refrigerant to a target pressure that is greater than 1 Bar based on the signals from the sensor being indicative that the pressure of the refrigerant is less than 1 Bar.

4. The thermal management system as claimed in claim 1 , wherein the memory contains instructions that are executable by the processor to: reduce power to the heater as the temperature of the refrigerant increases.

5. The thermal management system as claimed in claim 1 , wherein the memory contains instructions that are executable by the processor to:operate the heater at a selected output power until the temperature of the refrigerant is higher than a selected threshold temperature, reduce power to the heater as the temperature of the refrigerant increases, once the temperature of the refrigerant is higher than the selected threshold temperature.

6. A thermal management system as claimed in claim 1 , wherein the heater is part of a coolant-refrigerant heat exchanger that includes a coolant flow path for transporting coolant therethrough, and a refrigerant flow path for transporting refrigerant therethrough, wherein the coolant flow path and the refrigerant flow path are positioned in order to transfer heat from one of the coolant and the refrigerant to the other of the coolant and the refrigerant.

7. A thermal management system of a vehicle, the thermal management system including: a refrigerant circuit including a compressor, a condenser, a first branch that includes a first expansion valve and a first evaporator, and a second branch that includes a second expansion valve, and a second evaporator, wherein the second evaporator includes an air inlet and an air outlet in order to carry out heat exchange with ambient air, wherein the first branch and the second branch are fluidically in parallel with one another, wherein the refrigerant circuit is arranged to compress, condense, expand, and evaporate a refrigerant, wherein the heater is positioned to heat a first portion of the refrigerant in the first branch without heating a second portion of the refrigerant in the second branch, wherein the first and second branches end at a common outlet conduit so as to cause mixing of the first portion of the refrigerant and the second portion of the refrigerant; a control system including a processor and a memory, wherein the memory contains instructions that are executable by the processor for: a) operating the compressor to circulate the refrigerant in the refrigerant circuit; b) operating the heater to heat the refrigerant, and operating the second evaporator to carry out heat exchange with ambient air to heat the refrigerant;c) checking if a temperature of the refrigerant at an inlet to the first evaporator is less than an ambient air temperature minus a selected minimum temperature differential; and d) based on step c), reducing power to the secondary heater so as to maintain at least the selected minimum temperature differential between the temperature of the refrigerant at the inlet to the second evaporator and the ambient air temperature.

8. A thermal management system as claimed in claim 7, wherein the thermal management system includes a coolant circuit, that includes a pump, and a radiator, and wherein the first evaporator is a coolant-refrigerant heat exchanger that includes a coolant flow path for transporting coolant therethrough, a refrigerant flow path for transporting the first portion of the refrigerant therethrough, wherein the coolant flow path and the refrigerant flow path are positioned in order to transfer heat from one of the coolant and the refrigerant to the other of the coolant and the refrigerant, and wherein the heater is part of the coolant-refrigerant heat exchanger and is positioned to heat both the refrigerant and the coolant in the coolant-refrigerant heat exchanger.

9. A thermal management system, comprising: a refrigerant circuit including a compressor, a condenser, an expansion valve; and an evaporator, which are arranged to compress, condense, expand, and evaporate a refrigerant; a heater positioned to heat the refrigerant; a control system including a memory and a processor; and a sensor positioned to transmit signals to the control system that are indicative of a temperature of the refrigerant, wherein the memory contains instructions that are executable by the processor to: turn on the heater and operate the compressor sufficiently to raise the pressure of the refrigerant to at least a target pressure;determine if the temperature of the refrigerant is higher than a selected threshold temperature; and reduce power to the heater as the temperature of the refrigerant increases based on signals from the sensor, and based on whether the temperature of the refrigerant is higherthan the selected threshold temperature.

10. A method of controlling a compressor in a refrigerant circuit, comprising: determining a maximum allowable temperature for refrigerant at a first selected point in the refrigerant circuit; determining an actual temperature of the refrigerant at the first selected point in the refrigerant circuit; determining a first maximum allowable speed for the compressor based on the actual temperature of the refrigerant at the first selected point, and based on the maximum allowable temperature; determining a maximum allowable pressure for refrigerant at a second selected point in the refrigerant circuit; determining an actual pressure of the refrigerant at the second selected point in the refrigerant circuit; determining a second maximum allowable speed for the compressor based on the actual pressure of the refrigerant at the second selected point, and based on the maximum allowable pressure; using the lower of the first and second maximum allowable speeds as a final maximum allowable speed; determining a target temperature for the refrigerant at a third selected point in the refrigerant circuit; determining an actual temperature of the refrigerant at the third selected point in the refrigerant circuit; determining a target speed for the compressor based on the actual temperature of the refrigerant at the third selected point, and based on the target temperature;determining, at a first point in time that the target speed is lower than the final maximum allowable speed; operating the compressor at the target speed at the first point in time; determining, at a second point in time that the target speed is higher than the final maximum allowable speed; and operating the compressor at the final maximum allowable speed at the second point in time.11 . The method as claimed in claim 10, wherein the first selected point, the second selected point and the third selected point are all downstream from the compressor and upstream from the condenser.

12. The method as claimed in claim 10, wherein the determining of the first maximum allowable speed is carried out using a first PID control algorithm, wherein the determining of the second maximum allowable speed is carried out using a second PID control algorithm, and wherein the determining of the target speed is carried out using a third PID control algorithm.

13. A thermal management system of a vehicle, comprising: a refrigerant circuit including a compressor, a condenser, an expansion valve, and an evaporator, wherein the refrigerant circuit is arranged to compress, condense, expand, and evaporate a refrigerant; a heater positioned to heat the refrigerant downstream from the expansion valve and upstream from the compressor; and a control system including a memory and a processor, wherein the memory contains instructions that are executable by the processor for: determining a maximum allowable temperature for refrigerant at a first selected point in the refrigerant circuit;determining an actual temperature of the refrigerant at the first selected point in the refrigerant circuit; determining a first maximum allowable speed for the compressor based on the actual temperature of the refrigerant at the first selected point, and based on the maximum allowable temperature; determining a maximum allowable pressure for refrigerant at a second selected point in the refrigerant circuit; determining an actual pressure of the refrigerant at the second selected point in the refrigerant circuit; determining a second maximum allowable speed for the compressor based on the actual pressure of the refrigerant at the second selected point, and based on the maximum allowable pressure; using the lower of the first and second maximum allowable speeds as a final maximum allowable speed; determining a target temperature for the refrigerant at a third selected point in the refrigerant circuit; determining an actual temperature of the refrigerant at the third selected point in the refrigerant circuit; determining a target speed for the compressor based on the actual temperature of the refrigerant at the third selected point, and based on the target temperature; determining, at a first point in time that the target speed is lower than the final maximum allowable speed; operating the compressor at the target speed at the first point in time; determining, at a second point in time that the target speed is higher than the final maximum allowable speed; and operating the compressor at the final maximum allowable speed at the second point in time.

14. The thermal management system as claimed in claim 13, wherein the first selected point, the second selected point and the third selected point are all downstream from the compressor and upstream from the condenser.

15. The thermal management system as claimed in claim 13, wherein the determining of the first maximum allowable speed is carried out using a first PID control algorithm, wherein the determining of the second maximum allowable speed is carried out using a second PID control algorithm, and wherein the determining of the target speed is carried out using a third PID control algorithm.

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