Charging cycle strategy for vehicles using a cable with a smaller cross-section

Abstract

Vehicle charging system comprising: a conductive element configured to couple a charger (38) to a traction battery (24) and having a continuous current carrying capacity below a maximum charging current; characterized by a controller (76) programmed to control a current flow through the conductive element such that a current greater than the continuous current rating is conducted for less than a predetermined time based on an expected temperature increase of the conductive element caused by the current, wherein the current (200) and the predetermined time (206) are selected from a charging current profile, the charging current profile including a plurality of charging currents (200) and associated time values (206) configured to limit a temperature of the conductive element to less than a predetermined temperature.

Description

FIELD OF THE INVENTIONThe present application relates generally to charging vehicle batteries.GENERAL STATE OF THE ARTElectric and plug-in hybrid vehicles include a traction battery to provide power for propulsion and auxiliary loads. To function effectively, the traction battery must be charged when a state of charge of the battery falls below a threshold. A charger connected to an external power source may be coupled to the vehicle for the purpose of charging the traction battery. The charger may be connected to a charging port of the vehicle. The charger may provide a maximum battery charging current to the traction battery during charging. Conductive elements within the vehicle are configured to conduct the maximum battery charging current for an indeterminate period of time without a temperature of the conductive elements rising above a predetermined temperature. DE 10 2011 102 200 A1 discloses an electrical system of a motor vehicle having a traction battery, and methods for distributing electrical energy, and forms the generic prior art. DE 10 2011 008 674 A1, DE 10 2011 008 675 A1 and DE 10 2011 008 676 A1 disclose systems and methods for charging batteries in vehicles. DE 10 2011 005 991 A1 discloses a device and a method for checking a temperature sensor of a vehicle.SUMMARY OF THE INVENTIONAccording to the present invention, there is provided a vehicle charging system as claimed in claim 1, including a conductive member configured to couple a charger to a traction battery and having a continuous current load capacity below a maximum charging current. The vehicle charging system of the invention also includes a controller programmed to control a current flow through the conductive element such that a current greater than the continuous current loadability is conducted for less than a predetermined time based on an expected temperature increase of the conductive element caused by the current, the current and the predetermined time being selected from a charging current profile, the charging current profile including a plurality of charging currents and associated time values configured to limit a temperature of the conductive element to less than a predetermined temperature. The conductive element may be a conductor having a predetermined cross-sectional area. The conductive element may be a connector pin or a connector terminal. The conductive element may include a welded termination or a crimped termination. The predetermined time may decrease as the current increases. The predetermined time may be selected to limit a temperature rise of the conductive element to less than a predetermined temperature rise relative to an ambient temperature. The predetermined time may be further based on a cross-sectional area of the conductive element. The controller may be further programmed to decrease the current after the predetermined time. The current and the predetermined time are selected according to the invention from a charging current profile. According to the invention, the charging current profile includes a plurality of charging currents and associated time values configured to limit a temperature of the conductive element to less than a predetermined temperature.A vehicle useful in the practice of the claimed invention but not falling under the claimed invention includes a traction battery, a conductive element configured to couple a charge port to the traction battery and having a continuous current carrying capacity under a maximum charge current, and a controller. The controller is programmed to control a current flow through the conductive element such that a current greater than the steady state current carrying capacity is conducted for less than a predetermined time based on an expected temperature rise of the conductive element. The conductive element may be a conductor having a predetermined cross-sectional area. The conductive element may be a connector pin or a connector terminal. The predetermined time may decrease as the current increases. The predetermined time may be selected to limit a temperature rise of the conductive element to less than a predetermined temperature rise relative to an ambient temperature. The predetermined time may be further based on a cross-sectional area of the conductive element. The controller may be further programmed to decrease the current after the predetermined time.A method useful for practicing the claimed invention but not falling under the claimed invention includes coupling a traction battery to an external power source having a conductive element with a continuous current carrying capacity that is less than a maximum charging current of the traction battery. The method further includes controlling, by a controller, a current flow through the conductive element such that a current greater than the continuous current carrying capacity is conducted for less than a predetermined time based on an expected temperature rise of the conductive element. The predetermined time may be selected to limit a temperature rise of the conductive element to less than a predetermined temperature rise relative to an ambient temperature. Controlling the current flow may include decreasing the current after the predetermined time.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a diagram of a hybrid vehicle illustrating a typical driveline and energy storage components. FIG. 2 is a diagram of an example battery pack assembly that is comprised of multiple cells and monitored and controlled by a battery power control module. FIG. 3 is a diagram illustrating an example connection between a charge port and a traction battery. FIG. 4A is a diagram illustrating an example pin / terminal connection system using crimped connections. FIG. 4B is a diagram illustrating an example conductor connection system using a welded or soldered joint. FIG. 5 is a graph illustrating an example charging current profile.DETAILED DESCRIPTIONEmbodiments of the present invention are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure could be desired for particular applications or implementations.FIG. 1 shows a typical plug-in hybrid electric vehicle (PHEV) 12 The plug-in hybrid electric vehicle 12 may include one or more electric machines 14 mechanically connected to a hybrid transmission 16. The electric machines 14 may be capable of operating as a motor or as a generator. In addition, the hybrid transmission 16 is mechanically connected to an internal combustion engine 18. The hybrid transmission 16 is also mechanically connected to an input shaft 20 that is mechanically connected to the wheels 22. The electric machines 14 may provide propulsion and deceleration capability when the engine 18 is turned on or off. The electric machines 14 also act as generators and may provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric machines 14 may also reduce vehicle emissions by allowing the engine 18 to operate at more efficient speeds and by allowing the plug-in hybrid electric vehicle 12 to be operated in the electric motor when the engine 18 is off under certain conditions.A traction battery 24 or battery pack stores energy that may be used by the electric machines 14. A vehicle battery pack typically provides a high voltage DC output. The traction battery 24 is electrically connected to one or more power electronics modules 26. One or more contactors 42 may disconnect the traction battery 24 from other components when open and connect the traction battery 24 to other components when closed. The power electronics module 26 is also electrically connected to the electric machines 14 and provides the capability for bi-directional transfer of energy between the traction battery 24 and the electric machines 14. The power electronics module 26 may convert the DC voltage to a three-phase AC current for use by the electric machines 14. In a regenerative mode, the power electronics module 26 may convert the three-phase AC current from the electric machines 14 acting as generators to the DC voltage compatible with the traction battery 24. The description herein applies equally to a fully electric vehicle. For a fully electric vehicle, the hybrid transmission 16 may be a gearbox connected to an electric machine 14, and the engine 18 may not be present.In addition to providing energy for propulsion, the traction battery 24 may provide energy for other vehicle power systems. A typical system may include a DC / DC converter module 28 that converts the high voltage DC output of the traction battery 24 to a low voltage DC supply compatible with other vehicle loads. Other high voltage loads 46, such as compressors and electric heaters, may be directly connected to high voltage without the use of a DC-DC converter module 28. The low voltage systems may be electrically connected to an auxiliary battery 30 (e.g., 12 volt battery).The vehicle may be an electric vehicle or a plug-in hybrid vehicle 12 in which the traction battery 24 may be recharged by an external power source 36. The external power source 36 may be a connection to a power outlet that receives mains power. The external power source 36 may be electrically connected to an electric vehicle supply equipment (EVSE) 38. The EVSE 38 may provide circuitry and controls to regulate and manage the transfer of energy between the power source 36 and the vehicle 12. The external power source 36 may provide DC or AC electrical power to the EVSE 38. The EVSE 38 may have a charge connector 40 for plugging into a charge port 34 of the vehicle 12. The charge port 34 may be any type of port configured to transfer power from the EVSE 38 to the vehicle 12. The power conversion module 32 may condition the power supplied by the EVSE 38 to provide the proper voltage and current levels to the traction battery 24. The power conversion module 32 may couple to the EVSE 38 to coordinate the delivery of power to the vehicle. The EVSE connector 40 may have pins with recesses that couple to corresponding pins of the charge port 34. Alternatively, various components described as electrically connected may transfer power using wireless inductive coupling.One or more wheel brakes 44 may be provided to slow the vehicle and prevent movement of the vehicle. The wheel brakes 44 may be hydraulically or electrically actuated, or some combination thereof. The wheel brakes 44 may be part of a braking system 50. The brake system 50 may include other components to actuate the wheel brakes 44. For simplicity, the figure shows a single connection between the brake system 50 and one of the wheel brakes 44. The brake system 50 may include a controller for monitoring and coordinating the brake system 50. The brake system 50 may monitor the brake components and control the wheel brakes 44 for vehicle deceleration. The brake system 50 may be responsive to driver commands and may also operate autonomously to implement features such as stability control. The controller of the brake system 50 may implement a method of applying a requested braking force when requested by another controller or sub-function.One or more electrical loads 46 may be connected to the high voltage bus. The electrical loads 46 may have an associated controller that actuates and controls the electrical loads 46 when mounted. Examples of electrical loads 46 may be a heating module or an air conditioning module.The various components discussed may include one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., CAN (Controller Area Network)) or via discrete conductors. A system controller 48 may be present to coordinate the operation of the various components.A traction battery 24 may be constructed from a variety of chemical formulations. Typical battery pack chemistries may be lead acid, nickel metal hydride (NIMH), or lithium ions. FIG. 2 shows a typical traction battery pack 24 in a series configuration of N battery cells 72. however, other battery packs may be comprised of any number of individual battery cells connected in series or in parallel, or some combination thereof. A battery management system may include one or more controllers, such as a battery energy control module (BECM) 76, that monitors and controls the performance of the traction battery 24. The BECM 76 may monitor multiple battery pack level characteristics using various sensors and associated circuitry, which may include a pack current sensor 78, a pack voltage sensor 80, and a pack temperature sensor 82. The BECM 76 may have non-volatile memory so that the data may remain stored when the BECM 76 is in an off state. Stored data may be available on the next key cycle.In addition to the packet level characteristics, there may be battery cell 72 level characteristics that are measured and monitored. For example, the terminal voltage, the terminal current, and the temperature of each cell 72 may be measured. The battery management system may use a sensor module 74 to measure the characteristics of the battery cell 72. Depending on the capabilities, the sensor module 74 may include sensors and circuitry for measuring the characteristics of one or more of the battery cells 72. The battery management system may utilize up to N c sensor modules or Battery Monitor Integrated Circuits (BMICs) 74 to measure the characteristics of all battery cells 72. Each sensor module 74 may transmit the measurements to the BECM 76 for further processing and coordination. The sensor module 74 may transmit signals to the BECM 76 in analog or digital form. In some embodiments, the functionality of the sensor module 74 may be internally integrated with the BECM 76. That is, the sensor module 74 hardware may be incorporated as part of the circuitry in the BECM 76 and the BECM 76 may handle the processing of raw signals.The BECM 76 may include circuitry for coupling to one or more contactors 42. The positive and negative terminals of the traction battery 24 may be protected by contactors 42.FIG. 3 shows a diagram of a possible conductor connection between the charge port 34 and the traction battery 24. a conductor 100 may couple the traction battery 24 to the charge port 34. The conductor 100 may carry current to charge the traction battery 24. The conductor 100 may be a copper wire having a cross-sectional area. A first connection system 102 may connect the conductor 100 to the traction battery 24. A second connection system 104 may connect the conductor 100 to the charging port 34. The first connection system 102 and the second connection system 104 may be configured differently. Additional conductors may be present. In addition, other components or modules may be connected between the charge port 34 and the traction battery 24.The electrical strength of the vehicle charging system will be determined by parameters such as contact design (terminal / pin system), cable termination strategy (e.g., welding, crimping), and cable / conductor size. Generally, as the current capability of the system increases, the size and cost of the system also increases.Connections between and within components of the vehicle may be achieved using various conductive elements. The conductive members may include conductors such as wires and busbars. For example, a conductor may be a round copper wire having a cross-sectional area. The conductors are typically configured to transfer current for long periods of time at current levels at or below a confirmed steady state current loadability. That is, the conductor could operate indefinitely if the current flowing through the conductor is less than or equal to the steady state current carrying value. In a vehicle charging system, this design choice may result in conductors having a relatively large cross-sectional area. It is well known that as the cross-sectional area of the conductor increases the current resistance of the conductor. A conductor in the vehicle charging system may be sized based on a maximum rated charging current for the traction battery.FIG. 4A shows an example of a connector having a pin 108 and a terminal 110 in which the conductors 100, 116 are provided with a crimped termination 106 on the pin 108 and terminal 110. For example, conductor 100 may be part of charging port 34, while conductor 116 may be part of EVSE 38. A conductor 100 may be coupled using a connection system that may include a pair of connectors. The connectors may be comprised of two housings 112, 114 configured to interconnect such that when the housings 112, 114 are coupled together, corresponding conductive elements 108, 110 within each of the housings 112, 114 are in contact with each other. The conductive elements 108, 110 may be configured such that one of the housings 114 includes conductive pins 108, while the mating housing 112 may include conductive terminals 110 having a recess for receiving the pins 108. Typical connectors include terminals and pins configured to conduct a current with a steady state current rating for an indeterminate period of time. An additional consideration for connectors may be to ensure that the temperature of the connector remains below a predetermined temperature to prevent damage to the connector during operation.Various methods are available for terminating a conductor at a pin or terminal. A conductor 100 may be terminated by crimping to another conductive element. For example, a pin or terminal 108, 110 may provide a recess at one end for receiving the conductor 100, 116. The conductor 100, 116 may be inserted into the recess and a force may be applied to that portion of the pin / terminal surrounding the conductor to compress the pin or terminal around the conductor.FIG. 4B illustrates an example of a connector that includes a welded or soldered termination 122 to a terminal 124. The terminal 124 may be a conductive material defining a first opening. The terminal 124 may be placed in contact with a bus bar 126. The bus bar 126 may define a second opening that may be aligned with the first opening. A connecting member 128 may be inserted through the openings. A nut 130 or other means for securing the connector 128 may be used. When the nut 130 is tightened, the terminal 124 and the bus bar 126 may be in contact such that a current may flow from the conductor 100 to the bus bar 126. The connection between the conductor 100 and the terminal 124 may be a welded and soldered joint 122.Various combinations of the elements of FIGS. 4A and 4B may be used. Crimped terminations 106 and welded terminations 122 may be used interchangeably in the various configurations. The charging system described herein applies to connections within the charging port 34 and the traction battery 24, as well as to connections between the two. Note that FIGS. 4A and 4B illustrate examples of connection systems, and the described system is not limited to these illustrated examples.The traction battery 24 may be charged with a maximum battery charge current. The maximum battery charge current may be the maximum current that may be accepted by the traction battery 24 for charging. The traction battery 24 is not necessarily charged with the maximum battery charge current for an entire charging cycle. However, the conductive elements in the vehicle 12 are typically designed as though charging is continuous at the maximum battery charge current. A typical vehicle application may design the conductive elements between the charger 38 and the traction battery 24 such that the continuous current carrying capacity is at least equal to the maximum battery charging current.The continuous current load capacity for a conductive element is the amount of current that the conductive element can continuously conduct without exceeding a temperature that can damage the conductive element. The continuous current load capacity of a conductor can be influenced by a cross-sectional area of the conductor. For example, for a wire, the continuous current load capacity increases with the cross-sectional area of the wire. For connections between pins and terminals, other factors such as surface contact area may affect the persistent current loadability. The continuous current load capacity may be a maximum current that the conductive element can conduct for an unlimited period of time without a temperature of the conductive element becoming greater than a predetermined temperature at which the conductive element overheats.To reduce cost and size in a vehicle application, conductive elements having a continuous current carrying capacity less than the maximum battery charging current may be employed. For example, wires having a reduced cross-sectional area may be used so that the maximum battery charging current cannot be conducted indefinitely. However, the maximum battery charging current may be passed through the conductive element having a smaller cross-sectional area for a finite period of time rather than continuously. A charging current profile may be designed to limit the duration of maximum battery charging current based on the cross-sectional area of the conductor.The charging current profile may be a profile of current over time. While the continuous current load capacity of the conductive element is decreased, the time period during which the maximum battery charge current is conducted may be reduced. The charging current profile may be configured to prevent the temperature of the conductive element from increasing higher than a predetermined temperature that could damage the conductive element by overheating.Advantages of using conductive elements with a smaller cross-sectional area include lower cost and improved packaging of the conductive elements. The overall cost can be reduced because conductors and connectors may only need to meet the lower continuous current loads. The effect on charging power may be minimal as the traction battery 24 typically may not draw the maximum battery charge current continuously during a charging cycle.A battery management system may be configured to limit a temperature rise of the conductive elements to meet automotive standards. A control strategy may be implemented in a vehicle 12 that uses under-sized conductive elements to limit the temperature rise rate and the maximum temperature of the conductive elements. The control strategy may be configured to ensure that the conductive element having the lowest continuous current carrying capacity does not experience a temperature above a predetermined temperature. The current flowing through the conductive elements may be controlled to ensure that the temperature limits of the conductive elements are not exceeded.The temperature may be limited to rise by no more than a predetermined temperature above an ambient temperature to meet industry standards. For example, current industry standards allow for an increase of up to 50 degrees Celsius above ambient temperature. The standards may change in the future. The current profile for charging the traction battery may be configured to limit the temperature of the conductive elements to less than a predetermined temperature.The controller, such as the BECM 76, may be programmed to implement the charging current profile. The controller 76 may communicate with the EVSE 38 to control the amount of current flowing from the external power source 36 to the traction battery 24. The controller 76 may measure and monitor the actual current flowing through the traction battery 24. The actual or requested current may be used in conjunction with the current profile. Temperature sensors 82 may also be present to measure the temperature of the traction battery 24 and the conductive elements. The controller 76 may use the measured temperatures to limit the current to avoid excessive temperatures.FIG. 5 shows a possible current profile for charging the traction battery. The current profile may be a curve 200 of current over time. A maximum battery charge current 202 may be conducted for a limited period of time 206. After the limited time period 206, the current may be decreased. The continuous current load capacity 204 may be below the maximum battery charge current 202. Over time, the current may be decreased to less than the continuous current load capacity 204. The current profile can be derived from experimental data.As one example, a traction battery with a maximum battery charge current of 200 A may be configured to continuously process the full current. A conductor size of 50 mm 2 would allow the charging system to continuously flow 200 amps. However, a current of 200 amperes may be passed through a conductor having a cross-sectional area of 35 mm 2 for about 30 minutes before a temperature rise of 50 degrees Celsius from an ambient temperature. A controller may be implemented to allow the maximum battery charging current of 200 amps for less than 30 minutes. The current can be reduced after this time. In practice, the controller may reduce the current after a time of less than 30 minutes (e.g., 20 minutes) to allow some margin and component variations.The processes, methods, or algorithms disclosed herein may be provided to or implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or its own electronic control unit. Similarly, the processes, methods, or algorithms can be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, or algorithms can also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms can be embodied in whole or in part using suitable hardware components, such as application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software, and firmware components.It will be further described:A. A vehicle charging system comprising:a conductive member configured to couple a charger to a traction battery and having a continuous current load capacity under a maximum charging current; anda controller programmed to control a current flow through the conductive element such that a current greater than the steady state current carrying capacity is conducted for less than a predetermined time based on an expected temperature rise of the conductive element caused by the current.B. The vehicle charging system of A, wherein the conductive element is a conductor having a predetermined cross-sectional area.C. The vehicle charging system of A, wherein the conductive member is a connector pin or connector terminal.D. The vehicle charging system of A, wherein the conductive element includes a welded termination or a crimped termination.E. The vehicle charging system of A, wherein the predetermined time decreases as current increases.F. The vehicle charging system of A, wherein the predetermined time is selected to limit a temperature rise of the conductive member to less than a predetermined temperature rise relative to an ambient temperature.G. the vehicle charging system of A, wherein the predetermined time is further based on a cross-sectional area of the conductive element.H. The vehicle charging system of A, wherein the controller is further programmed to reduce the current after the predetermined time.I. The vehicle charging system of A, wherein the current and the predetermined time are selected from a charging current profile.J. The vehicle charging system of I, wherein the charging current profile includes a plurality of charging currents and associated time values configured to limit a temperature of the conductive element to less than a predetermined temperature.K. Vehicle comprising:a traction battery;a conductive member configured to couple a charge port to a traction battery and having a continuous current loadability under a maximum charge current; anda controller programmed to control a current flow through the conductive element such that a current greater than the steady state current carrying capability is conducted for less than a predetermined time based on an expected temperature rise of the conductive element.L. The vehicle of K, wherein the conductive element is a conductor having a predetermined cross-sectional area.M. The vehicle of K, wherein the conductive element is a connector pin or connector terminal.N. The vehicle of K, wherein the predetermined time decreases as current increases.O. The vehicle of K, wherein the predetermined time is selected to limit a temperature rise of the conductive member to less than a predetermined temperature rise relative to an ambient temperature.P. The vehicle of K, wherein the predetermined time is further based on a cross-sectional area of the conductive element.Q. The vehicle of K, wherein the controller is further programmed to decrease the current after the predetermined time.R. A method comprising:coupling a traction battery to an external power source with a conductive element having a continuous current carrying capacity that is less than a maximum charging current of the traction battery; andcontrolling, by a controller, a current flow through the conductive element such that a current greater than the continuous current carrying capacity is conducted for less than a predetermined time based on an expected temperature rise of the conductive element.S. The method of R, wherein the predetermined time is selected to limit a temperature rise of the conductive element to less than a predetermined temperature rise relative to an ambient temperature.T. The method of R, wherein controlling the current flow includes decreasing the current after the predetermined time.

Claims

A vehicle charging system comprising: a conductive member configured to couple a charger (38) to a traction battery (24) and having a continuous current load capacity below a maximum charging current; characterized a controller (76) programmed to control a current flow through the conductive element such that a current greater than the continuous current loadability is conducted for less than a predetermined time based on an expected temperature rise of the conductive element caused by the current, wherein the current (200) and the predetermined time (206) are selected from a charging current profile, the charging current profile including a plurality of charging currents (200) and associated time values (206) configured to limit a temperature of the conductive element to less than a predetermined temperature.The vehicle charging system of claim 1, wherein the conductive element is a conductor (100) having a predetermined cross-sectional area.The vehicle charging system of claim 1, wherein the conductive element is a connector pin (108) or a connector terminal (110).The vehicle charging system of claim 1, wherein the conductive element includes a welded termination (122) or a crimped termination (106).The vehicle charging system of claim 1, wherein the predetermined time (206) decreases with increasing current.The vehicle charging system of claim 1, wherein the predetermined time (206) is selected to limit a temperature rise of the conductive member to less than a predetermined temperature rise relative to an ambient temperature.The vehicle charging system of claim 1, wherein the predetermined time (206) is further based on a cross-sectional area of the conductive member.The vehicle charging system of claim 1, wherein the controller (76) is further programmed to reduce the current (200) after the predetermined time (206).

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