Variable precharge timing

An example method includes intentionally precharging a powertrain of an electric vehicle for an first time period that is different than a second precharge time period. An example electric vehicle assembly includes a precharge contactor transitionable back and forth between an open state and a closed state, a first main contactor, a second main contactor, and a controller configured to selectively close the second main contactor after the precharge contactor has been closed for a first time period that is different than a second precharge time period.

BACKGROUND

This disclosure relates generally to precharging when starting an electric vehicle. More particularly, this disclosure relates to varying a precharge time under some conditions, such as by increasing a time spent precharging.

Example electric vehicles include hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), and mild hybrid vehicles (mHEVs). Generally, hybrid vehicles differ from conventional vehicles because hybrid vehicles are selectively driven using a battery-powered electric machine. Conventional vehicles, by contrast, rely exclusively on an internal combustion engine to drive the vehicle.

An electrical power source, such as a battery, can be used to power a powertrain of an electric vehicle. Power from the battery is transferred to the electric machine. When the electric vehicle is off, the battery is disconnected from the rest of powertrain via contactors, for example. At start-up, the battery is reconnected to the portions of the powertrain.

The powertrain of an electric vehicle has significant capacitance. The capacitance has a very low resistance and can cause a large amount of in-rush current when the battery is reconnected and the capacitance charges. High in-rush current can damage components. Thus, many powertrains incorporate a precharge circuit to limit the in-rush current during the initial phase of start-up. The precharge circuit may incorporate a precharge contactor and resistor. The precharge circuit limits in-rush current by routing current through the precharge resistor.

As the capacitance is charged, the current decreases to a point where a main contactor, without the large resistance, can be connected. Prior art vehicles measure voltage to determine when to disconnect the precharge contactor.

SUMMARY

A method according to an exemplary aspect of the present disclosure includes, among other things, intentionally precharging a powertrain of an electric vehicle for a first time period that is different than a second precharge time period.

In another example of the foregoing method, the first time period is greater than the second precharge time period.

In another example of any of the foregoing methods, the first time period is an adjusted time period and the second time period is a baseline time period.

In another example of any of the foregoing methods, the method includes intentionally precharging in response to the electric vehicle starting remotely rather than not starting remotely.

In another example of any of the foregoing methods, the method further comprises intentionally precharging in response to the electric vehicle being unoccupied rather than occupied.

In another example of any of the foregoing methods, the method further comprises intentionally precharging in response to the electric vehicle charging.

In another example of any of the foregoing methods, the method further comprises stopping the precharging after both expiration of the first time period and a voltage differential falling below a threshold value.

In another example of any of the foregoing methods, the voltage differential is a voltage differential across a main contactor.

In another example of any of the foregoing methods, the first time period is used rather than the second precharge time period in response to at least one step in a start sequence completing before an allotted maximum time for the at least one step.

In another example of any of the foregoing methods, the second precharge time period is increased to the first time period an amount corresponding to a difference between the allotted maximum time for the at least one step and an actual time for the at least one step.

In another example of any of the foregoing methods, the at least one step includes at least a primary contactor close command step, a primary contactor closing step, a precharge contactor close command step, and a precharge contactor closing step.

In another example of any of the foregoing methods, the time spent precharging changes an in-rush current to the powertrain.

An electric vehicle assembly according to another exemplary aspect of the present disclosure includes, among other things, a precharge contactor transitionable back and forth between an open state and a closed state, and a controller configured to selectively keep the precharge contactor in the closed state for a first time period that is different than a second precharge time period.

In another example of the foregoing assembly, the first time period is greater than the second precharge time period.

In another example of any of the foregoing assemblies, the controller keeps the precharge contactor in the closed state for the first time period in response to the electric vehicle starting remotely rather than not starting remotely.

In another example of any of the foregoing assemblies, the controller is configured to transition a main contactor to a closed state after the first time period ends and a voltage differential falls below a threshold value. The main contactor in the closed state causing current to move through the main contactor rather than the precharge contactor.

In another example of any of the foregoing assemblies, the first time period is used rather than the second precharge time period when at least one step in a start sequence completes before an allotted maximum time for the at least one step. The first time period is greater than the second precharge time period by an amount representing a difference between the allotted maximum time for the at least one step and an actual time to complete the at least one step.

In another example of any of the foregoing assemblies, the time spent precharging changes an in-rush current to a powertrain of the electric vehicle.

In another example of any of the foregoing assemblies, the assembly includes a battery, a first main contactor having a first polarity, a second main contactor having a second polarity opposite the first polarity, and a precharge contactor. The controller is configured to transition the precharge contactor to the closed state to move current through the precharge resistor when the first main contactor is in a closed state and the second main contactor is in an open state.

In another example of any of the foregoing assemblies, the controller is configured to transition the second main contactor to the closed state in response to a delta voltage across the second main contactor that is less than a certain value.

In another example of any of the foregoing assemblies, a circuit between a battery and a motor is complete when the precharge contactor and the second main contactor are in a closed state, or when the first main contactor and the second main contactor are in the closed state.

In another example of any of the foregoing assemblies, the controller is a battery electric control module.

DETAILED DESCRIPTION

FIG. 1schematically illustrates a powertrain10for an electric vehicle. The powertrain10includes a battery14, a motor18, a generator20, and an internal combustion engine22.

Although depicted as a hybrid electric vehicle (HEV), it should be understood that the concepts described herein are not limited to an HEV and could extend to other electrified vehicles, including, but not limited to, plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs).

In one embodiment, the powertrain10is a power-split powertrain system that employs a first drive system and a second drive system. The first drive system includes a combination of the generator20and the engine22. The second drive system includes at least the motor18, the generator20, and a battery14. The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels26of the electric vehicle. The motor18and the generator20, together with a controller24, are an electric drive system28for the powertrain10.

The engine22and the generator20may be connected through a power transfer unit30, such as a planetary gear set. Other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine22to the generator20. In one non-limiting embodiment, the power transfer unit30is a planetary gear set that includes a ring gear32, a sun gear34, and a carrier assembly36.

The generator20can be driven by engine22through the power transfer unit30to convert kinetic energy to electrical energy. The generator20can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft38connected to the power transfer unit30. Because the generator20is operatively connected to the engine22, the speed of the engine22can be controlled by the generator20.

The ring gear32of the power transfer unit30may be connected to a shaft40, which is connected to vehicle drive wheels26through a second power transfer unit44. The second power transfer unit44may include a gear set having a plurality of gears46. Other power transfer units may also be suitable. The gears46transfer torque from the engine22to a differential48to ultimately provide traction to the vehicle drive wheels26. The differential48may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels26. In this example, the second power transfer unit44is mechanically coupled to an axle50through the differential48to distribute torque to the vehicle drive wheels26.

The motor18can also be employed to drive the vehicle drive wheels26by outputting torque to a shaft52that is also connected to the second power transfer unit44. In one embodiment, the motor18and the generator20cooperate as part of a regenerative braking system in which both the motor18and the generator20can be employed as motors to output torque. For example, the motor18and the generator20can each output electrical power to the battery14.

The battery14is an example type of electric vehicle battery assembly. The battery14may be a relatively high-voltage battery that is capable of outputting electrical power to operate the motor18and the generator20. Other types of energy storage devices and/or output devices can also be used with the powertrain10.

The powertrain controller24is operatively coupled to the internal combustion engine22, the electric drive system28, and the battery14. In some examples, the controller24is an inverter system controller combined with a variable voltage converter (ISC/VVC). In other examples, the controller24is part of an engine control module, a battery electric control module, etc. within the vehicle. The controller24is configured to control specific components within the electric drive system28, such as the generator20, the motor36, or both to support bidirectional power flow.

In this example, the controller24is configured to control a contactor assembly60to control current between the battery14and the remaining portions of the powertrain10, such as the motor18.

The example controller24includes a processor64operatively linked to a memory portion68. The example processor64is programmed to execute a program stored in the memory portion68. The program may be stored in the memory portion68as software code.

The program stored in the memory portion68may include one or more additional or separate programs, each of which includes an ordered listing of executable instructions for implementing logical functions.

The processor64can be a custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the controller24, a semiconductor-based microprocessor (in the form of a microchip or chip set) or generally any device for executing software instructions.

The memory portion68can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, VRAM, etc.)) and/or nonvolatile memory elements (e.g., ROM, hard drive, tape, CD-ROM, etc.). Moreover, the memory may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory can also have a distributed architecture, where various components are situated remotely from one another, but can be accessed by the processor.

Referring now toFIG. 2with continued reference toFIG. 1, the example contactor assembly60includes a first main contactor70, a second main contactor72, and a precharge contactor76. The contactors70,72, and76control current movement between the battery14and the motor18, the generator20, and other portions of the powertrain10. The contactor assembly60forms part of a circuit80between the battery14and the motor18.

In this example, the first main contactor70is associated with a negative terminal of the battery14, and the second main contactor72is associated with a positive terminal of the battery.

Capacitance within the powertrain10or circuit80is represented as a capacitor84inFIG. 2. If not accounted for, the capacitance will cause a large amount of in-rush current when the powertrain10is started. The in-rush current can damage components of the powertrain10. The contactor assembly60includes a resistor88used in connection with the precharge contactor76to reduce in-rush current on the circuit80.

Each of the contactors70,72, and76can be transitioned from an open state to a closed state and from the closed state to the open state. The controller24is configured to control the transitions of the contactors70,72, and76in this example.

When the first main contactor70and the second main contactor72have both transitioned to a closed state, current is free to move through the circuit80. When the precharge contactor78and the first main contactor70have both transitioned to a closed state, current is free to move through the circuit80.

Generally, when the powertrain10starts, the controller24transitions the precharge contactor76and the first main contactor70to closed. After the capacitor84has at least partially charged, the controller24transitions the second main contactor72to closed. The precharge contactor76could optionally transition to open at this stage.

Transitioning the precharge contactor76to closed at start-up, rather than the second main contactor72, causes current to be moved through the resistor88, which reduces in-rush current

Referring now toFIG. 3with continuing reference toFIGS. 1 and 2, the flow of example baseline method100for starting the electric vehicle is described. The method100is executed as a program by the processor64of the controller24.

The method100includes a step104of the controller24communicating a command to transition the first main contactor70to a closed state. A time T1is allocated for completing the step104. Next, at a step108, the method100allocates some time T2to close the first main contactor70. The controller24then sends a command to transition the precharge contactor76to a closed state at a step112, which takes a time T3.

At a step116, the method100allocates a time T4to close the precharge contactor76. The method100then moves to a step120where a time T5is spent precharging the capacitor84through the precharge contactor76, and thus the resistor88.

The method100then commands the second main contactor72to transition to closed at a step124, and includes a step128for the second main contactor72to close. The step124is allocated a time T6, and the step128is allocated a time T7.

In some examples, the method100may commands the precharge contactor76to transition to an open state at a step132, which takes a time T8. Opening the precharge contactor76is not required to complete the circuit80, however. Provided the first main contactor70and the second main contactor72are closed, the circuit80is complete.

The method100sends a message that the close of the circuit80is complete and opens the precharge contactor at the step132, which is allocated a time132.

The times T1to T8in connection with the method100are not to scale. In this example, the total of the times T1to T8does not exceed a target time for startup, such as no more than 400 milliseconds. Other targets are possible in other examples.

Given the target time for startup, baseline (or nominal) times for each of the steps104to132can be established, as well as maximum allowable time for each of the steps104to132. During startup, if any of the steps104to132exceed the maximum allowable time, an error may be generated and the startup stopped. A mechanical failure, for example, may cause on or more of the steps104to132to exceed the maximum allowable time.

Given the target time for startup, a person having skill in this art would be able to calculate the baseline time periods, and the maximum possible time periods for the steps104to132.

In one example, the time T5for the step120is nominally 110 milliseconds and has a maximum of 122 milliseconds.

To adjust the time spent precharging, the method100may intentionally adjust the time T5. In this example, the time T5is increased from a baseline precharge time period so that the powertrain10is intentionally precharged for an adjusted time period time rather than the baseline precharge time period T5. The adjusted time period, which is a first time period, is different than the baseline precharge time period T5, which is a second time period in this example.

In this disclosure, the baseline precharge time period refers to the time spent precharging during the baseline start sequence for the electric vehicle shown inFIG. 3. The baseline start sequence refers generally to the start sequence that is executed to start the electric vehicle when increasing the precharge time period is not possible or desirable.

In a first embodiment, the method100includes a step of determining if power to the wheels26of the powertrain10will be required within a set time after initiating the method100. If power is not required within one second, for example, the baseline precharge time period T5is increased to the adjusted precharge time period.

The method100may determine that power is not required within the set time if a user remotely starts a vehicle having the powertrain10, if the vehicle is unoccupied, or if the vehicle is charging. In such situations, power to the wheels of the powertrain10would not be required until a driver enters the vehicle.

In another embodiment of present disclosure, the method100stays at the step120for a maximum allowable time and then checks a voltage differential across the precharge contactor76. If the voltage differential is below a threshold value, such as 20 volts, the method100proceeds to the step124.

In the prior art methods, the voltage differential may have been checked, but after waiting a nominal amount of time, say 110 milliseconds, instead of a maximum allowable time of, for example, 122 milliseconds. This embodiment thus gains 12 milliseconds of precharging time. The adjusted time period is the maximum allowable time in this embodiment.

In another embodiment of the present disclosure, the method100calculates the actual time spent completing at least one of the steps104,108,112, and116. The difference or differences between the actual times completing the steps and the maximum allocated times T1to T4are then calculated as a total available difference.

The total available difference is then added to the time spent precharging, which increases the time spent precharging. Since the times T1and T4are maximum allowable times, the actual time for completing the steps104,108,112, and116is likely less than T1+T2+T3+T4. In this embodiment, the difference is used to desirably increase precharging time, while still keeping the total time spent conducting the method100at less than the total of T1to T8.

Relatively high in-rush currents can decrease the life of some components. Features of the disclosed examples includes increasing a time spent precharging an electric vehicle to increase the life of switching elements and other components of the powertrain.