WO2023223898A1

WO2023223898A1 - Method for starting a thermal management system for electric vehicles and thermal management system therefor

Info

Publication number: WO2023223898A1
Application number: PCT/JP2023/017446
Authority: WO
Inventors: Patrick Horn; Shivakumar Banakar; Ariel Marasigan; Julian Niedermayer; Dennis Wleklik
Original assignee: Denso Corporation; Denso Automotive Deutschland Gmbh
Priority date: 2022-05-19
Filing date: 2023-05-09
Publication date: 2023-11-23
Also published as: DE102022112574B3

Abstract

A thermal management system for electric vehicles is specified which, even at very low temperatures, can heat a vehicle cabin sufficiently without an electrical cabin heater. Heat from a coolant heater (220) and a compressor (10) is used for the cabin heating. The provision of a start-up procedure, which is divided into an optional first and a second start-up phase, enables the system to start up reliably. In the optional first start-up phase, compressor oil in an outside heat exchanger (40) is fed back into a refrigerant circuit so that it is again available for lubricating the compressor (10). In the second start-up phase, refrigerant condensed in the outside heat exchanger (40) is returned to the active refrigerant circuit.

Description

METHOD FOR STARTING A THERMAL MANAGEMENT SYSTEM FOR ELECTRIC VEHICLES AND THERMAL MANAGEMENT SYSTEM THEREFOR

Cross Reference to Related Application

This application is based on and incorporates herein by reference German Patent Application No. 102022112574.2 filed on May 19, 2022.

The disclosure relates to a method for starting a thermal management system and a thermal management system for carrying out this method.

Today's electric vehicles have a short range at low outside temperatures since a significant proportion of the electrical energy is used for heating the vehicle cabin. Heat pumps are now being used to reduce the use of electrical energy for heating the vehicle cabin.

The applicant offers such thermal management systems as a comparative example for electric vehicles with a heat pump assembly 1 that has the structure shown in Fig. 7. The heat pump assembly 1 connects a compressor 10 to a compressor inlet 11 and a compressor outlet 12 via a refrigerant circuit, a cabin condenser 20 for heating the air in a vehicle cabin with a condenser inlet 21 and a condenser outlet 22, an outside heat exchanger 40 for absorbing heat from or dissipating heat to the environment with an outdoor heat exchanger inlet 41 and an outdoor heat exchanger outlet 42, a chiller 80 or external evaporator with a chiller inlet 81 and a chiller outlet 82, wherein the chiller inlet 81 is connected to a chiller expansion valve 70, a cabin evaporator 60 with a cabin evaporator inlet 61 and a cabin evaporator outlet 62, wherein a cabin evaporator expansion valve 50 is upstream of the cabin evaporator inlet 61. On the air side, the cabin condenser 20 is provided with an air mix door 2 for temperature regulation. Optionally, an internal heat exchanger may be placed to transfer heat between the refrigerant before entrance to the cabin evaporator expansion valve 50 and the refrigerant after the cabin evaporator outlet 62. A bypass line 100 is provided between the outdoor heat exchanger outlet 42 and the compressor inlet 11 and can be shut off via a bypass shut-off valve 90. This refrigerant bypass line 100 is needed in heating or heat pump mode.

In order to heat the vehicle cabin sufficiently even at very low temperatures, an electrical cabin heater 300 is provided for the vehicle cabin. The thermal management system further comprises a battery 210 and an electric coolant heater 220. The electric coolant heater 220 is integrated into a coolant circuit 200 between the chiller 80 and the battery 210. Evaporation heat is supplied to the chiller 80 via the coolant circuit 200.

A valve unit 110 is arranged between the outdoor heat exchanger outlet 42 and the chiller expansion valve 70, on the one hand, and the outdoor heat exchanger inlet 41 and the condenser outlet 22, on the other hand. The valve unit 110 comprises a first and a

second refrigerant inlet

111, 113 and a first and a

second refrigerant outlet

112, 114. Optionally, a high-pressure-side refrigerant reservoir can be provided in the valve unit 110. Depending on the operating mode, the valve unit 110 blocks, directs, or throttles the refrigerant flows between the

refrigerant inlets

111, 113 and the

refrigerant outlets

112, 114. The heat pump assembly 1 or the thermal management system can be operated in various operating modes, such as a start or heating mode, by means of a controller 400.

In a heat pump or heating mode, refrigerant condensed by the cabin condenser 20 is supplied to the valve unit 110 via the first refrigerant inlet 111. Liquid refrigerant is then supplied to the chiller expansion valve 70 via the second refrigerant outlet 114, and the chiller expansion valve 70 generates a controlled expansion. The expanded refrigerant is vaporized in the chiller 80 by heat input via the coolant circuit 200 and compressed in the compressor 10. The compressed refrigerant gas from the compressor 10 is condensed in the cabin condenser, giving off heat to the air which is supplied to the vehicle cabin.

A disadvantage of the heat pump assembly according to Fig. 7 with refrigerants that are customary today, such as R134a or R1234yf, is that, at very low temperatures, -20°C and lower, they cannot completely cover the heat requirement for heating the vehicle cabin. This is due to the low suction pressure of the compressor 10 at very low temperatures. If the suction pressure drops, the density of the refrigerant decreases and thus the refrigerant mass flow for a given maximum volumetric flow rate of the compressor 10. This reduces the refrigerant mass flow and consequently the heat flow which is supplied to the vehicle cabin via the cabin condenser 20.

There are a number of ways to increase heating, such as gas injection systems, hot gas bypass heating systems, or electrical cabin heaters 300 shown in Fig. 7. The measures mentioned above entail additional costs and additional space, which is not always available.

Electrical heating elements

300 and 220 reduce the range of an electric vehicle. Various solutions for this are known from the prior art, for example from PLT 1, PLT 2, and PLT 3.

WO 2021/171802 A1 WO 2021/015483 A1 WO 2021/024755 A1

It is therefore the object of the present disclosure to heat the vehicle cabin sufficiently without an electrical cabin heater, even at very low temperatures in the range of -20°C.

Heat from the coolant heater and the compressor is used for the cabin heating. The provision of a start-up procedure, which is divided into an optional first and a second start-up phase, enables the system to start up reliably. In addition, damage to the compressor by liquid refrigerant from the outdoor heat exchanger and/or the chiller is prevented.

In the first start-up phase, compressor oil separated in the outside heat exchanger is returned to the active part of the refrigerant circuit for a first time period Δt₁, so that the compressor is adequately lubricated. The valve unit is switched to a first operating mode and connects the condenser outlet of the cabin condenser to the first refrigerant outlet of the valve unit and the outdoor heat exchanger outlet to the second refrigerant outlet of the valve unit. At very low outside temperatures, the gaseous refrigerant from the compressor condenses in the cabin condenser and liquefied refrigerant is fed to the outside heat exchanger. The compressor oil is flushed out of the outside heat exchanger with the liquid refrigerant and fed to the compressor.

The first start-up phase may be carried out at ambient temperatures <= -20°C. In the first start-up phase, the compressor may be operated in a lower speed range that is approx. 1/4 to 1/3 of the maximum speed. At ambient temperatures > -20°C, the first start-up phase can be omitted, i.e. Δt₁ = 0, and the start-up procedure begins with the second start-up phase.

In the second start-up phase, liquid refrigerant may be vaporized in the outside heat exchanger for a second period of time Δt₂and brought back into the refrigerant circuit through which it flows. This may take place in that the bypass shut-off valve in the bypass line is opened and the valve unit blocks the first refrigerant outlet and, at the same time, connects the refrigerant-side condenser outlet of the cabin condenser to the second refrigerant outlet. At the same time, the valve unit may terminate the connection between the outdoor heat exchanger outlet and the second refrigerant outlet. The blocked first refrigerant outlet of the valve unit may reduce the pressure in the outdoor heat exchanger, and liquid refrigerant in the outdoor heat exchanger vaporizes.

According to the above-described advantageous embodiment, in the second start-up phase, the compressor continues to be operated in the lower speed range during a first partial time period Δt₂₁ for safety reasons.

According to another embodiment, the speed of the compressor may be increased to a medium speed range (about 1/2 of the maximum speed) for a second partial period of time Δt₂₂, since hardly any more liquid refrigerant is suctioned out of the outside heat exchanger.

The second start-up phase may end when the pressure in the outside heat exchanger has dropped to the suction pressure at the compressor inlet. This may be the case after 60 to 180 seconds.

In an advantageous implementation, the bypass shut-off valve may be partially opened for a third partial time period Δt₂₃ and then fully opened for a fourth partial time period Δt₂₄ of the duration of the second start-up phase. The partial opening prevents the compressor from being exposed to an excessive quantity of liquid refrigerant.

This may be followed by the heating phase in which at least heat from the electric coolant heater and waste heat from the compressor are used to heat the vehicle cabin. To switch to the heating phase, the bypass shut-off valve in the bypass line may be closed. In this case, the valve unit continues to be operated according to the second start-up phase.

In the heating phase, heat from the outside heat exchanger can preferably also be used to heat the cabin. To this end, the bypass shut-off valve may be opened and the refrigerant mass flow may be adjusted through the variable opening cross-section at the first refrigerant outlet of the valve unit in such a way that a desired overheating of the refrigerant results downstream of the outside heat exchanger.

Depending on the heating capacity requirement of the cabin, the compressor may also be operated at an upper speed range during the heating phase.

According to another embodiment, a thermal management system may be provided which enables operation with the first and/or second start-up phase and in the heating phase.

According to an advantageous embodiment, a refrigerant collector may be provided on the high-pressure side as part of the valve unit or upstream of the compressor on the low-pressure side. Depending on requirements, the refrigerant collector means that more or less refrigerant is actively available in the refrigerant circuit or refrigerant is buffered for the different operating modes of the heat pump assembly. There is also a separation between the liquid and gaseous refrigerant in the refrigerant collector. Finally, refrigerant losses are balanced out by small leaks as the service life of the heat pump assembly progresses.

Further details, features, and advantages of the disclosure result from the following description of a preferred embodiment of the disclosure.

Fig. 1 shows the structure of the heat pump assembly which is an essential part of a thermal management system for vehicles; Fig. 2 shows the time sequence of the various phases; Fig. 3 shows the thermal management system in a first start-up phase in which compressor oil returns to the heat pump circuit; Fig. 4 shows the thermal management system in a second start-up phase in which refrigerant returns to the heat pump circuit; Fig. 5 shows the thermal management system in the heating phase; Fig. 6 shows a second embodiment of the disclosure with a low-pressure-side refrigerant collector; and Fig. 7 shows the structure of a thermal management system according to a comparative example.

Fig. 1 shows the structure of a heat pump assembly 1 which is an essential part of a thermal management system for vehicles. The thermal management system according to Fig. 1 differs from the thermal management system according to Fig. 7 only by the absence of the electric cabin heating and by the special design of the controller 400, which enables operation in the first and/or second start-up phase and in the heating phase. In the first start-up phase, liquid compressor oil is returned from the outside heat exchanger 40 to the heat pump circuit. In the second start-up phase, liquid refrigerant in the outdoor heat exchanger 40 is returned to the compressor inlet via the bypass line 100 by evaporation. In the heating phase, low-grade heat from the coolant circuit 200 is coupled into the chiller 80 and this heat is released, together with waste heat from the compressor 10, at a higher pressure and temperature level than the condensation heat in the cabin condenser 20 in order to heat the vehicle cabin.

Fig. 2 shows the timing of the two start-up phases and the heating phase together with the heating output of the electric coolant heater 220, the speed of the compressor 10, the state of the bypass shut-off valve 90 in the bypass line 100, the switching state of the valve unit 110, and the refrigerant pressure in the outside heat exchanger 40 with the suction pressure at the compressor inlet 11.

In the first start-up phase shown in Fig. 3, the electric coolant heater 220 and the compressor 10 are switched on. The compressor 10 is operated at a lower speed range (about 1/4 to 1/3 of the maximum speed). The low speed prevents any liquid refrigerant fed into the compressor from causing damage. By means of the refrigerant circuit, low-grade heat from the electric coolant heater 220 is coupled into the chiller 80 via the coolant circuit 200. The bypass shut-off valve 90 in the bypass line 100 is closed. The valve unit 110 is in a switching state I. In switching state I, the connection is enabled between the first refrigerant inlet 111 and the first refrigerant outlet 112 and between the second refrigerant inlet 113 and the second refrigerant outlet 114. In addition, the connection between the first refrigerant inlet 111 and the first refrigerant outlet 112 is activated. At low outside temperatures, for example -20°C, the gaseous refrigerant from the compressor 10 condenses completely in the cabin condenser 20 and in the outside heat exchanger 40. The liquid refrigerant from the cabin condenser 20 and the outside heat exchanger 40 flushes the compressor oil into the chiller 80. Due to the heat from the electric coolant heater 220 coupled into the chiller 80 via the coolant circuit 200, the refrigerant in the chiller 80 vaporizes and the compressor oil is fed to the compressor 10, whereby it is lubricated. The active parts of the refrigerant circuit are shown in bold in Fig. 3. The first start-up phase should be carried out at ambient temperatures <= -20°C. The lower the ambient temperature, the longer the first start-up phase takes. At ambient temperatures > -20°C, the first start-up phase can be omitted, i.e. Δt₁ = 0, and the start-up procedure begins with the second start-up phase.

In the second start-up phase shown in Fig. 4, liquid refrigerant is vaporized in the outside heat exchanger 40 for a second period of time Δt₂and brought back into the refrigerant circuit through which it flows. The transition from the first start-up phase to the second start-up phase takes place in that the bypass shut-off valve 90 in the bypass line 100 is partially opened and the valve unit 110 is switched to switching state II. In switching state II, the first refrigerant outlet 112 is blocked, the connection between the second refrigerant inlet 113 and the second refrigerant outlet 114 is terminated, and the connection between the first refrigerant inlet 111 and the second refrigerant outlet 114 is enabled. If the first start-up phase is dispensed with, the bypass shut-off valve 90 is opened so that the outdoor heat exchanger outlet 42 is connected to the compressor inlet 11. The first refrigerant outlet 112 is blocked. The valve unit 110 enables the connection between the first refrigerant inlet 111 and the second refrigerant outlet 114 in switching state II of the valve unit 110.

As a result, the refrigerant pressure in the outdoor heat exchanger 40 drops and liquid refrigerant in the outdoor heat exchanger 40 is vaporized. This is carried out for a first partial time period Δt₂₁until the pressure in the outdoor heat exchanger 40 has dropped to the suction pressure at the compressor inlet 11. After that, for a second partial time period Δt_22,the speed of the compressor 10 is increased to a medium speed range, which is approx. 1/2 of the maximum speed, and the suction pressure and the pressure in the outdoor heat exchanger 40 continue to drop, so that liquid refrigerant in the outdoor heat exchanger 40 further vaporizes. The second start-up phase ends after Δt₂= Δt_{21 +}Δt₂₂= 60 to 180 seconds. Alternatively, the second start-up phase may end when superheated refrigerant is present at the compressor inlet 11. The second period of time Δt₂ may be determined in that the pressure in the external heat exchanger 40 has adjusted to the suction pressure of the compressor 10.

In an advantageous implementation, the bypass shut-off valve 90 is partially opened for a third partial time period Δt₂₃ and then fully opened for a fourth partial time period Δt₂₄ of the duration of the second start-up phase. The partial opening prevents the compressor from being exposed to an excessive quantity of liquid refrigerant. The first and third partial periods of time and the second and fourth partial periods of time can be the same.

The active parts of the refrigerant circuit are shown in bold in Fig. 4. The refrigerant discharge from the outside heat exchanger 40 is shown in dotted lines.

This is followed by the heating phase shown in Fig. 5, in which at least heat from the electric coolant heater 220 and waste heat from the compressor 10 are used to heat the vehicle cabin. To switch from the second start-up phase to the heating phase, the controller 400 causes the bypass shut-off valve 90 in the bypass line 100 to be closed and the valve unit 110 to remain in switching state II.

At higher ambient temperatures, additional thermal energy can be absorbed from the environment via the outside heat exchanger 40. To do this, the bypass shut-off valve 90 must be open and the valve unit 110 regulates the overheating of the refrigerant downstream of the outside heat exchanger 40 via the degree of opening of the first refrigerant outlet 112.

The compressor 10 is operated in an upper speed range up to the maximum speed. The controller 400 regulates the thermal management system such that the condensation temperature in the cabin condenser 20 enables a desired temperature in the vehicle cabin. This is done using the speed of the compressor 10 as a manipulated variable. The refrigerant gas in the chiller 80 is overheated by the degree of opening of the chiller expansion valve 70 as a manipulated variable.

Optionally, a refrigerant collector 4 can be provided upstream of the compressor 10 on the high-pressure side as part of the valve unit 110 or on the low-pressure side. Depending on requirements, the refrigerant collector 4 means that more or less refrigerant is actively available in the refrigerant circuit or refrigerant is buffered for the different operating modes of the heat pump assembly 1. There is also a separation between the liquid and gaseous refrigerant in the refrigerant collector 4. Finally, refrigerant losses are compensated for by small leaks as the service life of the heat pump assembly 1 progresses.

In the high-pressure-side arrangement of the refrigerant collector 4 with a refrigerant collector inlet 5 and a refrigerant collector outlet 6 as part of the valve unit 110, which is not shown, the refrigerant collector inlet 5 is connected to the refrigerant-side condenser outlet 22 via the first refrigerant inlet 111 or to the outside heat exchanger outlet 42 via the second refrigerant inlet 113, and the refrigerant collector outlet 6 is connected to the second refrigerant outlet 114. This arrangement is described in DE 102022104545.5, filed on 25 February 2022. With regard to the arrangement of the refrigerant collector 4, reference is made in full to DE 102022104545.5.

In the low-pressure-side arrangement of the refrigerant collector 4 upstream of the compressor 10 according to Fig. 6, the refrigerant collector outlet 6 with the compressor inlet 11 and the refrigerant collector inlet 5 is connected to the chiller outlet 82 and the bypass shut-off value 90. Fig. 6 differs from Fig. 1 only in the refrigerant collector 4 being upstream of the compressor 10.

Claims

A method for starting a thermal management system for electric vehicles, the thermal management system comprising a battery (210), an electric coolant heater (220), a heat pump assembly (1) and a controller (400),
wherein the heat pump assembly (1) comprising a compressor (10) with a compressor inlet (11) and a compressor outlet (12), a cabin condenser (20) with a refrigerant-side condenser inlet (21) and a refrigerant-side condenser outlet (22), an external heat exchanger (40) with refrigerant-side external heat exchanger inlet (41) and refrigerant-side outdoor heat exchanger outlet (42), a chiller expansion valve (70) and a chiller (80) with refrigerant-side chiller inlet (81) and refrigerant-side chiller outlet (82), a valve unit (110) and a bypass line (100) with a bypass shut-off valve (90) between the outdoor heat exchanger outlet (42) and the compressor inlet (11),
wherein the valve unit (110) is connected via a first refrigerant inlet (111) to the condenser outlet (22), via a first refrigerant outlet (112) to the outdoor heat exchanger inlet (41), via a second refrigerant inlet (113) to the outdoor heat exchanger outlet (42), and is connected to the chiller expansion valve (70) via a second refrigerant outlet (114), and
wherein the electric coolant heater (220) is integrated into a coolant circuit (200) between the battery (210) and the chiller (80),
the method comprising steps:
s0) activating the electric coolant heater (220);
s1) operating the heat pump assembly (1) in an optional first start-up phase s2) and a non-optional second start-up phase s3), whereas
s2) operating the heat pump assembly (1) for a first period of time (Δt₁) in the first start-up phase, during which heat from the coolant circuit (200) evaporates refrigerant at a lower pressure level in the chiller (80), refrigerant compressed in the compressor (10) condenses at an upper pressure level in the cabin condenser (20) with heat dissipation air to be supplied to a vehicle cabin, and the liquid refrigerant is supplied via the valve unit (110), the external heat exchanger (40) and again to the chiller expansion valve (70); and
s3) reducing the pressure in the outdoor heat exchanger (40) for a second period of time (Δt₂) in the second start-up phase by opening the bypass shut-off valve (90) in the bypass line (100) and simultaneously closing the first refrigerant outlet (112) and by releasing the connection between the first refrigerant inlet (111) and the second refrigerant outlet (114) by means of the valve unit (110).
The method according to claim 1, characterized in that the first start-up phase is dispensed with at ambient temperatures > -20°C by setting the first period of time (Δt₁) at zero.
The method according to claim 1 or 2, characterized in that the compressor (10) is operated in a lower speed range in step s2) and during a first partial period of time (Δt₂₁) in step s3).
The method according to one of the preceding claims, characterized in that the compressor (10) is operated in a medium speed range during a second partial time period (Δt₂₂) in step s3).
The method according to any one of the preceding claims, characterized in that the second period of time (Δt₂) is determined in that the pressure in the external heat exchanger (40) has adjusted to the suction pressure of the compressor (10).
Method according to one of the preceding claims, characterized in that the bypass shut-off valve (90) is partially opened for a third partial time period (Δt₂₃) and then fully opened for a fourth partial time period (Δt₂₄).
The method according to any one of the preceding claims, characterized in that after the end of the first and/or second start-up phase, there is a transition into a heating phase in which heat from the coolant circuit (200) evaporates refrigerant at a lower pressure level in the chiller (80), the refrigerant compressed in the compressor (10) condenses at an upper pressure level in the cabin condenser (20) while dissipating heat to a vehicle cabin, and the liquid refrigerant is fed back to the chiller expansion valve (70) via the valve unit (110).
The method according to claim 7, characterized in that in the heating phase the bypass shut-off valve (90) is also opened and the refrigerant mass flow from the first refrigerant outlet (112) through the valve unit (110) is adjusted such that a desired superheating of the refrigerant after the external heat exchanger (40) at the refrigerant-side external heat exchanger outlet (42) is achieved, whereby ambient heat is coupled into the cabin condenser (20) via the external heat exchanger (40) and the compressor (10).
The method according to claim 7 or 8, characterized in that the compressor (10) is operated in the heating phase at an upper speed range.
A thermal management system for electric vehicles for carrying out the method according to one of the preceding claims, the thermal management system comprising:
a battery (210), an electric coolant heater (220), a heat pump assembly (1) and a controller (400), the heat pump assembly (1) having a compressor (10) with a refrigerant-side compressor inlet (11) and a refrigerant-side compressor outlet (12), a Cabin condenser (20) with refrigerant-side condenser inlet (21) and refrigerant-side condenser outlet (22), an outside heat exchanger (40) with refrigerant-side outside heat exchanger inlet (41) and refrigerant-side outside heat exchanger outlet (42), a chiller expansion valve (70) and a chiller (80) with refrigerant-side Chiller inlet (81) and refrigerant-side chiller outlet (82), a valve unit (110), and a bypass line (100) with a bypass shut-off valve (90) between the outdoor heat exchanger outlet (42) and the compressor inlet (11),
wherein the valve unit (110) has a first refrigerant inlet (111) which is connected to the condenser outlet (22), a first refrigerant outlet (112) connected to the outdoor heat exchanger inlet (41), a second refrigerant inlet (113) connected to the outdoor heat exchanger outlet (42), and a second refrigerant outlet (114) connected to the chiller expansion valve (70),
wherein the electric coolant heater (220) is integrated into a coolant circuit (200) between the battery (210) and the chiller (80), and
wherein the controller (400) is configured to operate the thermal management system in the optional first and the non-optional second start-up phase and in the heating phase.
The thermal management system according to claim 10, characterized in
that the valve unit (110) comprises a refrigerant collector (4) with a refrigerant collector inlet (5) and a refrigerant collector outlet (6) on the high-pressure side,
that the valve unit (110) connects the refrigerant collector inlet (5) via the first refrigerant inlet (111) to the refrigerant-side condenser outlet (22) or via the second refrigerant inlet (113) to the outdoor heat exchanger outlet (42), and
that the valve unit (110) connects the refrigerant collector outlet (6) to the second refrigerant outlet (114).
The thermal management system according to claim 10, characterized in
that the heat pump assembly (1) comprises on the low-pressure side a refrigerant collector (4) comprising a refrigerant collector inlet (5) and a refrigerant collector outlet (6),
that the refrigerant collector outlet (6) is connected to the compressor inlet (11), and
that the refrigerant receiver inlet (5) is connected to the chiller outlet (82) and the bypass shut-off valve (90).