Traction battery pack charge and discharge operations

Abstract

The present disclosure provides traction battery pack charge and discharge operations. A traction battery pack operation method includes charging a traction battery pack of an electrically powered vehicle. The charging includes charging a first sub-pack of battery cells together with a second sub-pack of battery cells. The method may include separately discharging the first sub-packet and the second sub-packet. The method may include maintaining the at least one switch in an off state during the discharge to electrically isolate the first sub-packet from the second sub-packet.

Description

Technical Field

[0001] The present disclosure relates generally to a traction battery pack, and more particularly to charging and discharging a traction battery pack. Background Art

[0002] Electrified vehicles differ from conventional motor vehicles in that they can be selectively driven by one or more electric motors powered by a traction battery pack. The electric motors can propel the vehicle in place of, or in combination with, an internal combustion engine. The traction battery pack discharges while powering the electric motor or motors and other loads in the electrified vehicle. Summary of the Invention

[0003] In some aspects, the technology described herein relates to a traction battery pack operating method, comprising: charging a traction battery pack of an electrified vehicle, the charging comprising charging a first subpack of battery cells and a second subpack of battery cells together; and discharging the first subpack and the second subpack separately.

[0004] In some aspects, the technology described herein relates to a method wherein the first subpack of battery cells is a first subpack of battery cells having a lithium metal anode and wherein the second subpack of battery cells is a second subpack of battery cells having a lithium metal anode.

[0005] In some aspects, the technology described herein relates to a method that also includes maintaining at least one switch in an open state to electrically isolate the first sub-pack from the second sub-pack during the discharging.

[0006] In some aspects, the technology described herein relates to a method that also includes providing power from the first sub-pack to a load and electrically isolating the second sub-pack from the load when the first sub-pack and the second sub-pack are separately discharged.

[0007] In some aspects, the technology described herein relates to a method that also includes transitioning at least one switch to electrically isolate the second sub-packet from the load.

[0008] In some aspects, the technology described herein relates to a method wherein the load is at least one motor of the electrified vehicle.

[0009] In some aspects, the technology described herein relates to a method that also includes switching from discharging the first sub-packet and the second sub-packet separately to discharging the second sub-packet separately from the first sub-packet.

[0010] In some aspects, the technology described herein relates to a method that also includes precharging the second sub-packet during the switching.

[0011] In some aspects, the technology described herein relates to a method in which the discharging is performed during a drive cycle.

[0012] In some aspects, the techniques described herein relate to a method that also includes switching based on a health status in the first sub-packet, the second sub-packet, or both.

[0013] In some aspects, the technology described herein relates to a method that also includes switching based on a driving mode of the electrified vehicle.

[0014] In some aspects, the technology described herein relates to a method that also includes switching based on a range of the electrified vehicle reaching a threshold range when discharging from the first subpack.

[0015] In some aspects, the technology described herein relates to a method wherein separately discharging the first sub-packet and the second sub-packet includes discharging the first sub-packet into a load without discharging the second sub-packet into the load.

[0016] In some aspects, the technology described herein relates to a method that also includes dividing the traction battery pack into the first subpack of battery cells and the second subpack of battery cells, wherein dividing the traction battery pack into the first subpack and the second subpack includes electrically isolating the second subpack from both the first subpack and a load.

[0017] In some aspects, the technology described herein relates to a method wherein the traction battery pack is an 800 volt traction battery pack, wherein the first sub-pack is 400 volts and the second sub-pack is 400 volts.

[0018] In some aspects, the technology described herein relates to a method, further comprising dividing the traction battery pack into the first subpack of battery cells and the second subpack of battery cells, wherein the dividing further comprises dividing the traction battery pack into at least one third subpack, and the discharging is of the first subpack without discharging the second subpack or the at least one third subpack.

[0019] In some aspects, the technology described herein relates to a method wherein the first sub-pack and the second sub-pack are both retained within a battery housing.

[0020] In some aspects, the technology described herein relates to a traction battery assembly, comprising: a traction battery pack that powers a load; and a switch system, the switch system being configured to transition between a charging state, a first discharge state, and a second discharge state, wherein when the switch system is in the charging state, a first sub-pack of battery cells in the traction battery pack and a second sub-pack of battery cells in the traction battery pack are both configured to be charged, when the switch system is in the first discharge state, the first sub-pack is electrically connected to the load and the second sub-pack is electrically isolated from the load, and when the switch system is in the second discharge state, the second sub-pack is electrically connected to the load and the first sub-pack is electrically isolated from the load.

[0021] In some aspects, the technology described herein relates to a traction battery assembly wherein the switch system electrically isolates the first subpack of battery cells from the second subpack of battery cells when the switch system is in the first discharge state and when the switch system is in the second discharge state.

[0022] In some aspects, the technology described herein relates to a traction battery assembly wherein the first subpack of battery cells is a first subpack of battery cells having lithium metal anodes, and wherein the second subpack of battery cells is a second subpack of battery cells having lithium metal anodes.

[0023] The embodiments, examples and alternatives of the preceding paragraphs, claims or following description and drawings, including any of their various aspects or corresponding individual features, may be taken independently or in any combination. Features described in conjunction with one embodiment apply to all embodiments, unless such features are incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] According to the detailed description, various features and advantages of the disclosed examples will become apparent to those skilled in the art. The drawings accompanying the detailed description can be briefly described as follows:

[0025] Figure 1 A side view of an electrified vehicle according to an exemplary aspect of the present disclosure is shown.

[0026] Figure 2 Shown Figure 1 Expanded view of the traction battery pack for an electrified vehicle.

[0027] Figure 3 Shows the operation Figure 2 A flow chart of an exemplary method for a traction battery pack.

[0028] Figure 4 Shown Figure 2Schematic diagram of a traction battery pack when operating in a charging state in which a first sub-pack of the traction battery pack and a second sub-pack of the traction battery pack are charged together.

[0029] Figure 5 Shown Figure 2 Schematic diagram of a traction battery pack when operating in a first discharge state in which a first sub-pack supplies power to a load and a second sub-pack is isolated from both the load and the first sub-pack.

[0030] Figure 6 Shown Figure 2 Schematic diagram of a traction battery pack when operating in a second discharge state in which the second sub-pack supplies power to the load and the first sub-pack is isolated from both the load and the second sub-pack. DETAILED DESCRIPTION

[0031] The traction battery pack of an electrified vehicle may include battery cells that are charged and discharged. The battery cells may be charged, for example, from an external power source or, if the electrified vehicle is a hybrid electric vehicle, from the electrified vehicle's generator. The battery cells may be discharged to power one or more traction motors or other loads of the electrified vehicle. Charging and discharging at different rates may extend the life of some types of battery cells, such as those with lithium metal anodes.

[0032] refer to Figure 1 and Figure 2 In an exemplary, non-limiting embodiment, the electrified vehicle 10 includes a traction battery pack 14 that powers an electric motor 18. The electrified vehicle 10 also includes wheels 22 driven by the electric motor 18. The traction battery pack 14 can power the electric motor 18, which converts electricity into torque to drive the wheels 22.

[0033] The electrified vehicle 10 is a pure electric vehicle. In other examples, the electrified vehicle 10 is a hybrid electric vehicle that can selectively use torque provided by an internal combustion engine (as an alternative to or in addition to the electric motor) to drive the wheels. In general, the electrified vehicle 10 can be any type of vehicle having a traction battery pack.

[0034] The traction battery pack 14 includes a housing 30 that encloses a plurality of battery arrays 34. Each of the battery arrays 34 includes a plurality of individual battery cells 38, which, in this example, have lithium metal anodes. Such battery cells 38 can provide relatively high energy density and extend their cycle life by discharging at a rate significantly higher than their charge rate. Battery cells with lithium metal anodes can include battery cells with liquid electrolytes, battery cells with solid electrolytes, or some combination thereof.

[0035] Now refer to Figures 3 to 6 And continue to refer to Figure 1 and Figure 2 The method 100 for operating the traction battery pack 14 generally includes a step 104 of charging the traction battery pack 14. Step 104 may include charging the traction battery pack 14 from a power source 40, which may be an external power source such as a charging station. In another example, the charging may be from one or more generators of the electrified vehicle 10.

[0036] Charging includes charging a first sub-pack 62 of battery cells 38 and a second sub-pack 64 of battery cells 38. In this example, both the first sub-pack 62 and the second sub-pack 64 are retained within the housing 30.

[0037] In this example, the first subpack 62 may include two of the battery arrays 34. The second subpack 64 may include two of the remaining battery arrays 34. If the traction battery pack 14 is an 800-volt pack, the first subpack 62 and the second subpack 64 may each be 400 volts. In other examples, battery packs with other voltages may be used, including 1200-volt packs.

[0038] Charging of the first subpack 62 and the second subpack 64 can occur when the first subpack 62 and the second subpack 64 are connected in parallel or in series. Charging when the first subpack 62 and the second subpack 64 are connected in series as an 800 volt battery pack can reduce the current required to meet the charging power target.

[0039] In this example, the battery cells 38 of the first sub-pack 62 and the battery cells 38 of the second sub-pack 64 have the same chemistry (i.e., nickel manganese cobalt (NMC), lithium iron phosphate (LFP), or nickel cobalt aluminum (NCA)). In other examples, the battery cells 38 of the second sub-pack 64 have different chemistries. The chemistry need not be the same, but the voltage scale between the first sub-pack 62 and the second sub-pack 64 is typically similar.

[0040] During charging, the switch system 70 electrically connects the first sub-pack 62 and the second sub-pack 64. In this example, the switch system 70 includes switches S1, S2, S3, and S4. Switches S1 and S2 are closed during charging. Switches S3 and S4 are open.

[0041] In one embodiment, a control module 74 (such as a vehicle controller) executes the method 100 by controlling the transitions of the switch system 70. However, other configurations and other types of controls are contemplated within the scope of the present disclosure. Although schematically illustrated as a single control module 74, multiple control modules may be operably linked and configured to function together to facilitate various monitoring and control strategies associated with the traction battery pack 14 having the first sub-pack 62 and the second sub-pack 64.

[0042] The control module 46 may include a processor 78 and non-transitory memory 82 for executing various control strategies and modes associated with the method 100. The processor 78 may be a custom or commercially available processor, a central processing unit (CPU), or generally any device for executing software instructions. The memory 82 may include a combination of volatile memory elements and non-volatile memory elements.

[0043] The processor 78 may be operably coupled to the memory 82 and may be configured to execute one or more programs stored in the memory 82 of the control module 74 based on various inputs received from other devices such as the switches S1 , S2 , S3 , S4 and various sensors within or external to the traction battery pack 14 .

[0044] At step 108 , after charging, the method 100 divides the traction battery pack 14 into a first subpack 62 of battery cells 38 and a second subpack 64 of battery cells 38 . Figure 5 The exemplary method 100 schematically illustrated in FIG. 1 changes the switch system 70 to partition the traction battery pack 14 in this manner. Specifically, switches S1 and S3 are closed, while switches S2 and S4 are open. Switches S1, S2, S3, and S4 are maintained in these states while discharging from the first subpack 62.

[0045] This configuration of the switch system 70 effectively electrically isolates the first sub-pack 62 from the second sub-pack 64 and the load 86. This configuration of the switch system 70 electrically couples the first sub-pack 62 to the load 86. The load 86 may be the electric machine 18, other high-voltage loads of the electrified vehicle 10, or both. At step 112, the method 100 then discharges the first sub-pack 62 but not the second sub-pack 64.

[0046] When Figure 5 In the illustrated configuration, the switch system 70 is considered to be in a first discharge state. In the first discharge state, the first sub-pack 62 is discharged by supplying power to the load 86. The second sub-pack 64 is electrically isolated from the load and the first sub-pack 62. Therefore, the second sub-pack 64 is not discharged, and the first sub-pack 62 is discharged separately from the second sub-pack.

[0047] At step 116, method 100 stops discharging from the first sub-pack 62 and begins discharging from the second sub-pack 64. This may occur in response to a triggering event, such as the state of charge within the first sub-pack 62 dropping to a threshold state of charge, eg, ten percent.

[0048] The switch system 70 is reconfigured to make this change. Figure 6The switching system 70 is schematically shown being switched so that the second subpack 64 is discharging rather than the first subpack 62. To make this change, switches S1 and S2 are switched to or maintained in an open state, while switches S3 and S4 are switched to or maintained in a closed state.

[0049] In some examples, method 100 includes pre-charging the second sub-pack 64 to suppress electrical issues associated with inrush current when switching from discharging from the first sub-pack 62 to discharging from the second sub-pack. Pre-charging can involve a circuit with a power resistor to limit inrush current, or a DC / DC converter to compensate for imbalance between the first sub-pack 62 and the second sub-pack 64.

[0050] Step 116 may occur while the electrified vehicle 10 is moving during a drive cycle. In some examples, the triggering event that prompts the method 100 to begin discharging from the second sub-pack 64 rather than the first sub-pack 62 may be based on the driving mode. For example, discharging from the first sub-pack 62 may occur when the electrified vehicle 10 is operating in a front-wheel drive mode, and discharging from the second sub-pack 64 may occur when the electrified vehicle 10 is operating in an all-wheel drive mode.

[0051] In some examples, the first sub-pack 62 is designated to power one or more motors of the electrified vehicle 10 , and the second sub-pack 64 is designated to power one or more other motors of the electrified vehicle 10 .

[0052] Another exemplary triggering event may include the health of the first sub-packet 62, the second sub-packet 64, or both. Another triggering event may include the level of thermal energy within the first sub-packet 62, the second sub-packet 64, or both. Switching from discharging from the first sub-packet 62 to discharging from the second sub-packet 64 may provide time for the thermal energy to dissipate from the first sub-packet 62.

[0053] Yet another exemplary triggering event may be the range of the electrified vehicle 10 when powered by the first sub-pack 62. For example, the switch at step 116 may occur when the electrified vehicle 10 has reached a threshold range for traveling while powered by the first sub-pack 62. For example, the switch from discharging from the first sub-pack 62 to the second sub-pack 64 may occur when the range of the electrified vehicle 10 when powered by the first sub-pack 62 drops below fifty miles.

[0054] The switching at step 116 may alternatively or additionally occur based on the desired state of charge of the first sub-pack 62 and the second sub-pack 64 upon arrival at the destination. For example, if it is desired to arrive at the destination with substantially equal state of charge in both the first sub-pack 62 and the second sub-pack 64, the switching may occur midway through the journey to the destination. This may help the vehicle 10 arrive at the destination with both the first sub-pack 62 and the second sub-pack 64 at substantially the same temperature, state of charge, etc.

[0055] It will be appreciated that, if necessary, method 100 may include switching back to discharging from the first sub-pack 62. Furthermore, if, for example, power demand is particularly high, method 100 may include simultaneously discharging from both the first sub-pack 62 and the second sub-pack 64. For example, this may be in response to the electrified vehicle 10 climbing a hill.

[0056] While described with respect to dividing the traction battery pack 14 into a first subpack 62 and a second subpack 64, it should be understood that other divisions are possible. For example, the traction battery pack 14 may be further divided into at least a third subpack. That is, while described as being divided into two subpacks, the traction battery pack 14 may be divided into more than two subpacks.

[0057] In some examples, the control module 74 adjusts the cooling of the traction battery pack 14 in response to whether the first sub-pack 62 or the second sub-pack 64 is discharging. For example, when the first sub-pack 62 is discharging, more coolant can be directed to the heat exchange plates associated with the first sub-pack 62. In some examples, the cooling system can be sized to cool only the first sub-pack 62 or the second sub-pack 64. It will be appreciated that cooling will be directed to the first sub-pack 62 during discharge and then to the second sub-pack 64 during discharge.

[0058] Features of the disclosed examples include a traction battery pack that can be divided into discrete subpacks that are dynamically controlled to combine during vehicle charging but separate during discharge, allowing the vehicle to be operated independently from one subpack during driving. Additional subpacks can be included to, for example, optimize charge / discharge ratios or provide compatibility with future voltage standards. Partitioning the traction battery pack in this way can extend cycle life, particularly for lithium metal cells.

[0059] The foregoing description is illustrative rather than restrictive in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art, and such variations and modifications do not necessarily depart from the essence of the present disclosure. Therefore, the scope of protection afforded to the present disclosure should be determined solely by studying the appended claims.

Claims

1. A method for operating a traction battery pack, comprising: charging a traction battery pack of an electrified vehicle, the charging comprising charging a first subpack of battery cells together with a second subpack of battery cells; as well as The first sub-pack and the second sub-pack are discharged separately.

2. The method of claim 1 , wherein the first subpack of battery cells is a first subpack of battery cells having a lithium metal anode, and wherein the second subpack of battery cells is a second subpack of battery cells having a lithium metal anode. 3 . The method of claim 1 , further comprising maintaining at least one switch in an open state during the discharging to electrically isolate the first sub-pack from the second sub-pack.

4. The method of claim 1 , further comprising providing power from the first sub-pack to a load and electrically isolating the second sub-pack from the load when the first sub-pack and the second sub-pack are discharged separately, and optionally, further comprising transitioning at least one switch to electrically isolate the second sub-pack from the load.

5. The method of claim 4, wherein the load is at least one motor of the electrified vehicle, and optionally wherein both the first sub-pack and the second sub-pack are retained within a battery housing. The method of claim 1 , wherein the discharging is performed during a drive cycle.

7. The method of claim 1 , further comprising switching from discharging the first sub-packet and the second sub-packet separately to discharging the second sub-packet separately from the first sub-packet, and optionally, further comprising precharging the second sub-packet during the switching.

8. The method of claim 7, further comprising switching based on a health status in the first sub-packet, the second sub-packet, or both.

9. The method of claim 7, further comprising switching based on a driving mode of the electrified vehicle, switching based on when a range of the electrified vehicle reaches a threshold range when discharging from the first subpack, or both.

10. The method of claim 1, wherein separately discharging the first sub-packet and the second sub-packet comprises discharging the first sub-packet into a load without discharging the second sub-packet into the load.

11. The method of claim 1 , further comprising dividing the traction battery pack into the first subpack of battery cells and the second subpack of battery cells, wherein dividing the traction battery pack into the first subpack and the second subpack comprises electrically isolating the second subpack from both the first subpack and a load.

12. The method of claim 1, wherein the traction battery pack is an 800 volt traction battery pack, wherein the first subpack is 400 volts and the second subpack is 400 volts.

13. The method of claim 1 , further comprising dividing the traction battery pack into the first subpack of battery cells and the second subpack of battery cells, wherein the dividing further comprises dividing the traction battery pack into at least one third subpack, and the discharging is discharging the first subpack without discharging the second subpack or the at least one third subpack.

14. A traction battery assembly comprising: a traction battery pack, wherein the traction battery pack supplies power to a load; as well as a switching system configured to transition between a charging state, a first discharging state, and a second discharging state, When the switch system is in the charging state, the first subpack of battery cells in the traction battery pack and the second subpack of battery cells in the traction battery pack are both configured to be charged, When the switch system is in a first discharge state, the first sub-pack is electrically connected to the load, and the second sub-pack is electrically isolated from the load. When the switch system is in the second discharge state, the second sub-pack is electrically connected to the load, and the first sub-pack is electrically isolated from the load.

15. The traction battery assembly of claim 14 , wherein the switch system electrically isolates the first subpack of battery cells from the second subpack of battery cells when the switch system is in the first discharge state and when the switch system is in the second discharge state, and optionally, wherein the first subpack of battery cells is a first subpack of battery cells having lithium metal anodes and wherein the second subpack of battery cells is a second subpack of battery cells having lithium metal anodes.

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