A method for over-temperature protection of a compressor of a refrigeration cycle thermal conditioning circuit of a vehicle with an electric powertrain

Abstract

A method is described for the over-temperature protection of a compressor (EAC) of a refrigeration cycle thermal conditioning circuit (TCC1) of a vehicle (V) with an electric power unit, in which: - the compressor (EAC) is driven by means of a respective electric motor (MOT) operatively connected to a corresponding inverter (INV), - the refrigeration cycle thermal conditioning circuit (TCC1) comprises a condenser (CNDS) configured for the disposal of thermal power absorbed by a cooling fluid circulating in said refrigeration cycle thermal conditioning circuit (TCC1), - the vehicle comprises an air flow modulating device (AGS) disposed in front of the condenser (CNDS) with respect to a forward direction (FD) of the vehicle (V) and having a variable passage area configuration which gives rise to a first cooling air flow rate ( Is AI r AGS) through said capacitor (CNDS) variable from a minimum or zero value to a maximum value, - the vehicle (V) comprises a cooling fan (F) arranged behind the condenser (CNDS) with respect to the forward direction (FD) of the vehicle (V) and configured to supply a second cooling air flow (II LAR-fan) through said condenser (CNDS).

Description

[0001] A method for over-temperature protection of a compressor of a refrigeration cycle thermal conditioning circuit of a vehicle with an electric powertrain

[0002] TEXT OF THE DESCRIPTION

[0003] Field of the Invention

[0004] The present invention regards the vehicle with an electric powertrain, in particular BEVs. The invention was developed with particular reference to the thermal management of a refrigeration cycle thermal conditioning circuit, and specifically to the protection of said component from over-temperature events.

[0005] Prior Art

[0006] A refrigeration cycle conditioning system equipping a vehicle with an electric powertrain, in particular a BEV, is configured for the thermal conditioning - in particular for the cooling - of at least two critical environments of the vehicle: the passenger compartment and the high-voltage battery which powers one or more electric traction motors of the powertrain of the vehicle. For different reasons, meeting a temperature target for each of said environments is fundamental for the vehicle.

[0007] For this reason, the compressor which processes the refrigerant fluid in said thermal conditioning system has a size and a performance that lead to some thermal management problems which are generally uncommon in other types of vehicles other than BEVs, and which in any case do not find a solution also in BEVs.

[0008] The compressor is driven by an electric motor controlled by an inverter, which draws electrical power directly from the high-voltage battery of the vehicle. The cooling of the compressor, of the motor and of the inverter is performed both by an air flow rate, which is supplied through the radiant pack of the vehicle, and by a flow rate of refrigerant fluid which is processed by the compressor, such refrigerant fluid cooling the compressor internally and cooling the electric motor and the inverter by means of a heat exchange with an evaporation device of the refrigeration cycle circuit.

[0009] As regards the cooling by means of an air flow rate, the phrase "radiant pack" denotes an assembly of radiant elements for rejecting thermal energy, typically comprising a condenser of the refrigeration cycle thermal conditioning circuit and a radiator of a further thermal conditioning circuit of heat transfer fluid, generally arranged at the rear of the condenser in the direction of forward motion of the vehicle. Such air flow rate is substantially the result of three contributions to the supply, specifically: i) the vehicle motion, i.e. the forward motion of the vehicle ii) the action of the cooling fan, which is generally installed at the rear of the radiant pack with respect to a direction of forward motion of the vehicle iii) the passage section defined by an air flow rate modulation device, specifically a so-called AGS - Active Grille Shutter - located in front of the radiant pack with respect to a direction of forward motion of the vehicle.

[0010] The cooling of the compressor based on the combined action of the two processes described in the foregoing inevitably leads to the appearance of contrasting events in the thermal management of the compressor. If the flow rate of the cooling air - the control whereof depends on the layering of various needs - is not sufficient to cool the compressor, it is possible to increase the cooling contribution due to the flow rate of refrigerant fluid processed by the compressor. The increase of said flow rate, which can be obtained by means of an increase of the rotational speed of the compressor, improves the cooling of the compressor itself, since the refrigerant fluid processed by the compressor absorbs thermal power from it. However, the increase of the rotational speed of the compressor may increase the rejection of thermal power by the electric motor which actuates the compressor and by the related inverter due to the Joule effect, thus contrasting the cooling action of the air flow rate and of the refrigerant fluid flow rate, and increasing the risk of damages due to over-temperature of the compressor itself.

[0011] Object of the Invention

[0012] The invention aims at solving the technical problem outlined in the foregoing. Specifically, the object of the invention consists in providing a method for over- temperature protection of a compressor of a refrigeration cycle thermal conditioning circuit of a vehicle with an electric powertrain, which enables avoiding contrasting effects in the cooling of the compressor.

[0013] Summary of the Invention

[0014] The object of the invention is achieved by means of a method having the features set forth in the claims that follow, which form an integral part of the technical disclosure provided herein in relation to the invention.

[0015] Brief Description of the Figures

[0016] The invention will now be described with reference to the annexed Figures, which are provided by way of non-limiting example only and wherein:

[0017] - Figure 1 shows a block diagram representative of the method according to the invention,

[0018] - Figure 2 schematically shows a vehicle whereon it is possible to implement a method according to the invention, - Figure 3 shows a diagram representative of an aspect of the method according to the invention, and

[0019] - Figures 4 to 6 show implementation aspects of the method according to the present invention in preferred embodiments thereof.

[0020] Detailed Description

[0021] Referring to Figure 1, diagram 1, and to Figure 2, the invention defines a method for over-temperature protection of a compressor of a refrigeration cycle thermal conditioning circuit of a vehicle having an electric powertrain. Referring to Figure 2, the method may be applied to a vehicle V which comprises a first refrigeration cycle thermal conditioning circuit TCC1 and - optionally - a second thermal conditioning circuit with a heat transfer fluid TCC2, each comprising a respective radiant element for rejecting the thermal power absorbed by the respective circuit. The circuit TCC1 comprises a compressor EAC which is driven (in rotation) by a respective electric motor MOT operatively connected to a corresponding inverter INV, and it comprises - as a radiant element - a condenser CNDS configured for the rejection of thermal power absorbed by a refrigerant fluid circulating through the thermal conditioning circuit TCC1.

[0022] The vehicle V moreover comprises an air flow rate modulation device AGS located in front of the condenser CNDS with respect to a direction of forward motion FD of the vehicle V, and having a variable passage area configuration resulting in a first cooling air flow rate mAirAGS through the condenser CNDS varying from a minimum or zero value to a maximum value. The variable passage area configuration is implemented, for example, by means of a plurality of orientable vanes LV which can be rotated in such a way as to be aligned with the flow direction of the air flow rate mAirAGS, which determines a condition of a maximum passage area and of a maximum air flow rate, or else can be progressively inclined until they are orthogonal to the flow direction of the air flow rate or at any rate until they collectively define a shield with respect to the air flow rate corresponding to a condition of a minimum or null passage area and a minimum or null air flow rate.

[0023] Moreover, the vehicle V comprises a cooling fan F driven in rotation by means of an electric motor MF, which is located at the rear of the condenser CNDS with respect to the direction of forward motion FD of the vehicle V, and which is configured to supply a second cooling air flow rate through the condenser CNDS. Globally, as can be seen in the Figure, the condenser CNDS is impinged upon by a total air flow rate which corresponds to the sum of the contributions and

[0024] Always referring to Figure 2, the vehicle V preferably further comprises a second thermal conditioning circuit TCC2 with a heat exchange fluid, comprising - as a radiant element - a radiator RAD which is - always preferably, but not necessarily - located at the rear of the condenser CNDS with respect to the direction of forward motion FD, and in a position between the fan F and the condenser CNDS. Such an arrangement defines a radiant pack comprising the condenser CNDS and the radiator RAD, to which the flow rate is supplied; thus, said air flow rate impinges upon and traverses the condenser CNDS first, and then the radiator RAD.

[0025] This being said, and referring again to Figure 1, the method according to the invention includes:

[0026] - determining (block 2) a minimum admissible value of rotational speed of the compressor, as a function of a temperature of the electric motor MOT and of a temperature of the inverter INV,

[0027] - determining (block 4) a minimum admissible value of passage area of the modulation device AGS as a function of the temperature of the electric motor MOT and of the temperature of the inverter INV,

[0028] - determining (block 6) a minimum admissible value of rotational speed of the cooling fan F as a function of the temperature of the electric motor MOT and of the temperature of the inverter INV.

[0029] In other words, the invention aims at determining the values in such a way as to define a global operating point, for the components which influence the cooling of the compressor EAC, which enables avoiding damages due to over-temperature, thus also enabling avoiding the need of a derating. In this regard, referring to Figure 3, the diagram shown indicates by way of example three ranges of operational coordinates which correspond to three different ranges of temperatures of the compressor EAC and to three different intervention approaches for protecting the compressor EAC. The range A corresponds to operational coordinates for which the need of increasing the cooling of the compressor EAC is substantially non-existent. In other words, in the range A the absorption of electrical power by the compressor EAC is very low, or at any rate it can be rejected by the flow of refrigerant fluid and air of the current operating point, and it cannot generate a significant thermal load on the compressor (thereby meaning that the thermal load on the compressor EAC may be managed by the thermal capacity of the compressor EAC alone). Therefore, the rejection of thermal power due to the Joule effect by the motor MOT and by the inverter INV is correspondingly low, or at any rate it can be rejected by the flow of refrigerant fluid and air of the current operating point.

[0030] The range B corresponds to operational coordinates having values which are always higher than the values of the range A, and which require an increased cooling of the compressor EAC by means of the flow rate and the processing of the flow rate of refrigerant fluid by the same compressor EAC. In other words, in the range B the absorption of electrical power by the compressor EAC is at such levels as to increase the thermal load on the compressor EAC up to an amount which cannot be handled without a cooling action of the compressor and without generating a significant thermal load on the compressor itself, which cannot be managed by the thermal capacity of the compressor alone, nor be rejected by the flow of refrigerant fluid and air of the current operating point. In the same way, the rejection of thermal power due to the Joule effect by the motor MOT and the inverter INV increases, too, or anyway the possibility has decreased of rejecting the thermal power.

[0031] The range C corresponds to operational coordinates having values which are always higher than the values of the range B, and such as to make it necessary to operate a performance derating of the compressor EAC in order to avoid damages due to over- temperature, since it is not possible to reject all the thermal power absorbed by the compressor by means of the flow rate (in addition to the flow rate of refrigerant fluid processed by the compressor). In other words, in the range B the absorption of electrical power by the compressor EAC is at such levels as to increase the thermal load on the compressor EAC up to an amount which is always dangerous for the integrity of the compressor, thus such levels as to require a performance derating in order to reduce the amount of thermal power which must be rejected (which may even involve a shutdown) . In the same way, the rejection of thermal power due to the Joule effect by the motor MOT and the inverter INV is also increasing further with respect to the range B.

[0032] The object of the present invention consists therefore in preventing in any case excursions within the range B, remaining within the range B or even within the lower range A as much as possible.

[0033] There will now be described specific implementation aspects of preferred embodiments of the method according to the invention, referring to Figures 4 to 6.

[0034] Referring to Figure 4, diagram 10, the minimum admissible value of rotational speed of the compressor EAC is the greater (block 12, MAX) between a first minimum admissible value of rotational speed of the compressor EAC dependent on the temperature of the electric motor MOT, and a second minimum admissible value of rotational speed of the compressor EAC dependent on the temperature of the inverter INV.

[0035] Preferably, the value is determined by means of a map M14, which provides said value as a function of the temperature and similarly the value is determined by means of a map M16 which provides said value as a function of the temperature - Both maps qualitatively show an evolution of the Values and Which is constant up to a first knee K1 (which occurs at certain temperature values respectively, which are not necessarily identical to each other), then shows an increase from the first knee to a second knee K2 (which occurs at temperature values and which are higher than the values at which the first knee K1 occurs, and which are not necessarily identical to each other), and then is constant again after the second knee. Physically, this corresponds to the following circumstances: a) for values of the temperatures and lower than the values at which the first knee K1 occurs, the minimum values and which correspond to lower thresholds of rotational speeds in order to avoid over-temperature events of the compressor EAC, are very low, since the rejection of thermal power by the compressor EAC, by the motor MOT and by the inverter INV is very low, too, or at any rate it is not necessary to request an increase of flow rate of refrigerant fluid to a minimum value to cool the component (the compressor EAC). It is a set of circumstances which corresponds to the range A; b) for values of the temperatures TRefComp Mot and TRefcomp inv between the values of occurrence of the first knee K1 and the values of occurrence of the second knee K2, the minimum values and increase in a fashion substantially proportional to the increase of the values and In other words, the need arises to increase the cooling, and as regards the compressor EAC such a need can only be met by increasing the flow rate of refrigerant fluid which it processes (thus, by increasing the lower threshold of rotational speed). It is a set of circumstances with corresponds to the range B; c) above the temperature values and at which the second knee K2 occurs, an upper operational limit of rotational speed of the compressor EAC is reached, and therefore the capability to reject the thermal power by increasing the flow rate of refrigerant fluid is depleted, since a further increase of rotational speed would lead to an increase of the thermal power rejected by the motor MOT and by the inverter INV greater than the increase of cooling power, thus resulting in an overall worsening effect with respect to the purpose. The transition into said temperature ranges may bring about a transition into the range C (whether this occurs or not may depend, i.a., on the cooling contributions supplied by the device AGS and by the fan).

[0036] With reference to Figure 5, diagram 20, the minimum admissible value of passage area of the modulation device AGS (which corresponds, in the preferred embodiment, to a position of the vanes LV resulting in the minimum admissible value of said passage area) is the greater (block 22, MAX) of a first minimum admissible value of passage area of the modulation device AGS dependent on the temperature of the electric motor MOT and on a forward speed VehSpd of the vehicle, and a second minimum admissible value of passage area of said modulation device dependent on the temperature of the inverter INV and on the forward speed VehSpd of the vehicle.

[0037] Preferably, the value is determined by means of a map M24 which provides said value as a function of the temperature TRefcomp_Mot, and similarly the value is determined by means of a map M26 which provides said value as a function of the temperature TRefcomp inv- Both maps qualitatively show an evolution of the values Which is constant up to a first knee K1 (which occurs at certain temperature values respectively, which are not necessarily identical to each other), then increases from the first knee K1 to a second knee K2 (which occurs at temperature values TRefcomP_Mot and TRefcomP_inv which are higher than the values at which the first knee occurs, and which are not necessarily identical to each other), and then is constant again after the second knee. Each map, moreover, is parameterized with respect to different speed values VehSpd (thus, each map comprises a plurality of curves each being associated with a corresponding speed value VehSpd of the vehicle V), whereof, by way of example, four values VehSpd_1, VehSpd_2, VehSpd_3, VehSpd_4 are indicated, mentioned in an order of increasing forward speed of the vehicle V (thus, VehSpd_1 < VehSpd_2 < VehSpd_3 < VehSpd_4).

[0038] The evolution of the values and physically corresponds to the following circumstances: a) for temperature values lower than the values at which the first knee K1 occurs, the minimum Values which correspond to lower thresholds of passage area of the device AGS (thus of air flow rate in order to avoid over-temperature events of the compressor EAC, are very low, since the rejection of thermal power by the compressor EAC, as well as by the motor MOT and by the inverter INV, is very low too, or at any rate it is not necessary to request an increase of air flow rate to a minimum value to cool the component (the compressor EAC). Thus, a reduced (or even a null) air flow rate through the device AGS is sufficient. It is a set of circumstances which corresponds to the range A; b) for temperature values comprised between the values of occurrence of the first knee K1 and the values of occurrence of the second knee K2, the minimum values and increase in a fashion substantially proportional to the increase of the values and In other words, a need for cooling arises which, as regards the device AGS, may be met only by increasing the passage area, i.e. by "opening" the vanes LV. It is a set of circumstances which corresponds to the range B. It should be noted that the dependence of the values results in a shift of the second knee K2 towards values of the temperatures which increase with the increase of the speed of the vehicle. This means that, in the section between the knees K1 and K2, the values increase with the decrease of the forward speed of the vehicle since, under the same flow rate at low forward speeds a larger passage area in the device AGS is required, whereas at high forward speeds a smaller passage area in the device AGS is required; c) above the temperature values at which the second knee K2 occurs, the achievement occurs of the maximum passage area of the device AGS and of the maximum value of flow rate for the respective speed VehSpd.

[0039] Finally, referring to Figure 6, diagram 30, the minimum admissible value of rotational speed the cooling fan F is the greater (block 32, MAX) of a first minimum admissible value of rotational speed of the cooling fan dependent on the temperature of the electric motor MOT and on the vehicle forward speed VehSpd, and a second minimum admissible value of rotational speed of the cooling fan F dependent on the temperature of the inverter INV and on the vehicle forward speed VehSpd.

[0040] Preferably, the value is determined by means of a map M34 which provides said value as a function of the temperature and similarly the value is determined by means of a map M36 which provides said value as a function of the temperature Both maps qualitatively show an evolution of the values Which is constant up to a first knee K1 (which occurs at certain temperature values respectively, which are not necessarily identical to each other), then increases from the first knee K1 to a second knee K2 (which occurs at temperature values which are higher than the values at which the first knee occurs, and which are not necessarily identical to each other), and then is constant again after the second knee K2. Each map, moreover, is parameterized with respect to different values of the speed VehSpd (thus, each map comprises a plurality of curves and each being associated with a corresponding speed value VehSpd of the vehicle V) whereof, by way of example, the four values VehSpd_1, VehSpd_2, VehSpd_3, VehSpd_4 are indicated, which are mentioned in an order of increasing forward speed of the vehicle V (thus VehSpd_1 < VehSpd_2 < VehSpd_3 < VehSpd_4 ).

[0041] The evolution of the values and physically corresponds to the following circumstances: a) for temperature values lower than the values at which the first knee occurs, the minimum values which correspond to lower thresholds of rotational speed of the fan F (thus of air flow rate in order to avoid over-temperature events of the compressor EAC, are very low since the rejection of thermal power by the compressor EAC, as well as by the motor MOT and by the inverter INV, is very low as well, or at any rate it is not necessary to request an increase of air flow rate up to a minimum value to cool the component (the compressor EAC). Therefore, a reduced (or even a null) air flow rate processed by the fan F is sufficient. It is a set of circumstances which corresponds to the range A; b) for temperature values comprised between the values of occurrence of the first knee K1 and the values of occurrence of the second knee K2, the minimum values and increase in a fashion substantially proportional to the increase of the values and In other words, a need for cooling arises which, as regards the fan F, may be met only by increasing the rotational speed. It is a set of circumstances which corresponds to the range B.

[0042] It should be noted that the dependence of the values results in a Shift of the second knee K2 towards temperature values which increase with the increase of the vehicle speed. This means that, in the section between the knees K1 and K2, the values increase with the decrease of the forward speed of the vehicle since, under the same flow rate at low forward speeds, a higher rotational speed of the fan F is required, whereas at high forward speeds a lower rotational speed of the fan F is required; c) above the temperature values and at which the second knee K2 occurs there is reached the maximum value of rotational speed admitted for the fan F, and the maximum value of flow rate for the respective speed VehSpd. Generally speaking, it is preferable to reach the maximum rotational speed of the fan F only after having fully exploited the passage area of the device AGS.

[0043] The knees are denoted with the same references - K1 and K2 - throughout the Figures. However, in no case shall this be construed as implying the fact that the knees K1 and K2 occur in the same temperature conditions of the motor MOT and of the inverter INV for all maps under consideration (as it is already evident from the maps M24, M26 and M34, M36).

[0044] Thanks to the method according to the invention it is possible to achieve an over-temperature protection of the compressor EAC of a refrigeration cycle thermal conditioning circuit TCC1 of a vehicle V with an electric powertrain, while avoiding contrasting effects in cooling the compressor. The definition of the minimum values defines, as stated in the foregoing, an optimal global operating point for the components which influence the cooling of the compressor EAC, avoiding both the contrasting effects and the damages due to over- temperature.

[0045] Of course, the implementation details and the embodiments may amply vary with respect to what has been described and illustrated, without departing from the extent of the present invention, as defined in the annexed claims.

Claims

CLAIMS1. A method for the overtemperature protection of a compressor (EAC) of a refrigeration cycle thermal conditioning circuit (TCC1) of a vehicle (V) with an electric powertrain, wherein:- the compressor (EAC) is driven by a respective electric motor (MOT) operatively connected to a corresponding inverter (INV), the refrigeration cycle thermal conditioning circuit (TCC1) includes a condenser (CNDS) configured for the rejection of thermal power absorbed by a refrigerant fluid circulating through said refrigeration cycle thermal conditioning circuit (TCC1), the vehicle (V) includes an air flow rate modulation device (AGS) located in front of the condenser (CNDS) with respect to a direction of forward motion (ED) of the vehicle (V) and having a variable passage area configuration resulting in a first cooling air flow rate through said condenser (CNDS) varying froma minimum or zero value to a maximum value, the vehicle (V) comprises a cooling fan (F) located at the rear of the condenser (CNDS) with respect to the direction of forward motion (ED) of the vehicle (V) and configured to supply a second cooling air flow ratethrough said condenser (CNDS), the method including:- determining (2) a minimum admissible value of rotational speed of the compressor(EAC) as a function of a temperature of saidelectric motor (MOT) and a temperature of said inverter (INV),- determining (4) a minimum admissible value of passage areaof said air flow rate modulation device (AGS) as a function of the temperature of said electric motor (MOT) and thetemperature of said inverter (INV),- determining (6) a minimum admissible value of rotational speedof the cooling fan (F) as a function of the temperatureof said electric motor (MOT) and the temperature ofsaid inverter (INV).

2. The method of claim 1, wherein the minimum admissible value of rotational speedof the compressor (EAC) is the greater (12) of a first minimum admissible value of rotational speedof the compressor (EAC) dependent on the temperature of said electric motor (MOT)and a second minimum admissible value of rotational speedof the compressor (EAC) depending on the temperature of said inverter (INV).

3. The method of claim 1 or claim 2, wherein the minimum admissible value of passage area of said air flow rate modulation device(AGS) and is the greater (22) of a first minimum admissible value of passage area ) ofsaid air flow modulation device (AGS) dependent on the temperatureof said electric motor (MOT) and a vehicle forward speed (VehSpd) and a second minimum admissible value of passage area ofsaid air flow rate modulation device (AGS) dependent on the temperature of said inverter (INV) andsaid vehicle forward speed (VehSpd).

4. The method of any of the foregoing claims, wherein said minimum admissible value of rotational speed of the cooling fan (F) is thegreater (32) of a first minimum admissible value of rotational speed of the cooling fan(F) dependent on the temperature of saidelectric motor (MOT) and a vehicle forward speed (VehSpd) and a second minimum admissible value of rotational speedof the cooling fan (F) dependent on the temperatureof said inverter (INV) and said vehicle forward speed (VehSpd).

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