Auxiliary power supply for hybrid electric vehicles

Abstract

The present disclosure relates to auxiliary power supplies for hybrid electric vehicles. A vehicle includes a first electric machine configured to generate low voltage power. The vehicle includes a second electric machine configured to generate high voltage power. The vehicle includes a power converter configured to convert the high voltage power generated by the second electric machine to the low voltage power. The vehicle includes a controller configured to: in response to a low voltage power demand exceeding a limit of the power converter, operate the first electric machine and the power converter to satisfy the low voltage power demand; in response to the power converter being operable, in an instance in which the low voltage power demand does not exceed the limit of the power converter, operate only the power converter to satisfy the low voltage power demand.

Description

TECHNICAL FIELD

[0001] This application relates generally to power sources in hybrid electric vehicles configured to supplement power to a low voltage power bus. BACKGROUND

[0002] Hybrid electric vehicles (HEVs) utilize components that draw power from a high voltage power bus and a low voltage power bus. Power for the low voltage power bus originates from the high voltage power bus. When insufficient power can be transferred from the high voltage power bus to the low voltage power bus, a battery connected to the low voltage power bus can temporarily provide power but will eventually be depleted. Once the battery is depleted, components that draw power from the low voltage power bus become inoperable. SUMMARY

[0003] A vehicle includes a first electric machine configured to generate low voltage power. The vehicle also includes a controller configured to: (i) in response to a low voltage power demand exceeding a limit of a power converter, operate the first electric machine and the power converter to meet the low voltage power demand, the power converter configured to convert high voltage power generated by a second electric machine to low voltage power; (ii) in response to the power converter being operable, in an instance in which the low voltage power demand does not exceed the limit of the power converter, operate only the power converter to meet the low voltage power demand.

[0004] The controller can also be configured to operate the first electric machine to generate an amount of power that is a difference between the low voltage power demand and the limit. The controller can also be configured to operate only the first electric machine to meet the low voltage power demand in response to the power converter being unable to convert high voltage power to low voltage power. The controller can also be configured to operate the first electric machine to generate an amount of power that is a lesser of the low voltage power demand and a power limit of the first electric machine. The controller can also be configured to operate the first electric machine to start an engine connected to the first electric machine in response to the low voltage power demand exceeding the limit and the engine stopping. The controller can also be configured to operate an engine connected to the first electric machine at a rotational speed that is at least a predetermined rotational speed configured to cause the first electric machine to generate an amount of power that meets the low voltage power demand. The limit can be less than a maximum possible low voltage power demand. A sum of the limit and a power capacity of the first electric machine can be at least equal to a maximum possible low voltage power.

[0005] A method includes converting, by a power converter, high voltage power generated by a first electric machine to low voltage power. The method also includes operating the power converter and a second electric machine in response to a low voltage power demand exceeding a limit of the power converter, where the second electric machine is configured to generate low voltage power. The method also includes operating only the power converter to meet the low voltage power demand in response to the power converter being operable in the event that the low voltage power demand does not exceed the limit of the power converter.

[0006] The method can also include operating the second electric machine to start an engine connected to the second electric machine in response to the low voltage power demand exceeding the limit and the engine stopping. The method can also include operating only the second electric machine to generate low voltage power in response to the power converter being unable to convert high voltage power to low voltage power. An amount of power generated by the second electric machine can be a lesser of the low voltage power demand and a power limit of the second electric machine. The method can also include operating an engine connected to the second electric machine at a rotational speed of at least a predetermined rotational speed configured to cause the second electric machine to generate an amount of low voltage power that meets the low voltage power demand. The method can also include starting the engine in response to the engine connected to the second electric machine stopping. The limit can be less than a maximum possible low voltage power demand.

[0007] A vehicle includes a first electric machine configured to generate low voltage power and a power converter configured to convert high voltage power generated by a second electric machine to low voltage power. The vehicle also includes a controller configured to operate the first electric machine to generate an amount of power that meets a low voltage power demand in response to the power converter being unable to convert high voltage power to low voltage power.

[0008] The controller can also be configured to operate the first electric machine to generate the amount of power that is a lesser of the low voltage power demand and a power limit of the first electric machine. The controller can also be configured to operate the first electric machine and the power converter to meet the low voltage power demand in response to the power converter being unable to convert high voltage power to low voltage power and the low voltage power demand exceeding a limit of the power converter. The limit can be less than a maximum possible low voltage power demand. The operating the first electric machine can include operating an engine configured to drive the first electric machine at a rotational speed of at least a predetermined rotational speed configured to cause the first electric machine to generate the amount of power. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a block diagram of a vehicle having a hybrid powertrain system.

[0010] Figure 2 is a diagram of a low voltage power distribution system for a vehicle.

[0011] Figure 3 is a flowchart of a feasible sequence of operations for operating a supplemental power source under certain conditions. DETAILED DESCRIPTION

[0012] Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various forms and alternate forms. The drawings are not necessarily to scale; the dimensions of some features can have been exaggerated or minimized for the proper clarity of the present disclosure. 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 embodiments. As those skilled in the art will appreciate, the various features shown and described either with respect to any figure can be combined with features shown and described in one or more other figures, to produce embodiments that are not explicitly shown or described. The combinations of features are deemed to be within the scope of the present disclosure. The combinations of features are deemed to be within the scope of the present disclosure.

[0013] Referring to Figure 1 , a schematic diagram of a hybrid electric vehicle (HEV) 110 is shown in accordance with embodiments of the present disclosure. Figure 1 A representative relationship between components is shown. The physical arrangement and orientation of components within a vehicle can vary. The HEV 110 includes a powertrain 112. The powertrain 112 includes an engine 114 that drives a transmission 116, which can be referred to as a modular hybrid transmission (MHT). As will be described in greater detail below, the transmission 116 includes an electric machine, such as an electric motor / generator (M / G) 118, an associated traction battery 120, a torque converter 122, and a multi-speed stepped-ratio automatic transmission or gear box 124.

[0014] Both engine 114 and M / G 118 are drive sources for HEV 110. Engine 114 generally represents a power source that can include an internal combustion engine, such as a gasoline, diesel, or natural gas powered engine, or a fuel cell. Engine 114 generates engine power and corresponding engine torque that is supplied to M / G 118 when a decoupling clutch 126 between engine 114 and M / G 118 is at least partially engaged. M / G 118 can be implemented by any of a variety of types of electric machines. For example, M / G 118 can be a permanent magnet synchronous motor. As will be described below, a power electronics module 156 conditions direct current (DC) power provided by traction battery 120 to meet the requirements of M / G 118. For example, the power electronics module can provide three-phase alternating current (AC) to M / G 118.

[0015] Power flow from engine 114 to M / G 118 or from M / G 118 to engine 114 is possible when decoupling clutch 126 is at least partially engaged. For example, decoupling clutch 126 can be engaged and M / G 118 can operate as a generator to convert rotational energy provided by crankshaft 128 and M / G shaft 130 into electrical energy that will be stored in traction battery 120. Decoupling clutch 126 can also be disengaged to isolate engine 114 from the rest of powertrain 112 so that M / G 118 can be used as the sole drive source for HEV 110. M / G shaft 130 extends through M / G 118. M / G 118 is continuously drivingly connected to shaft 130, however engine 114 is only drivingly connected to M / G shaft 130 when decoupling clutch 126 is at least partially engaged.

[0016] The M / G 118 is connected to the torque converter 122 via the M / G shaft 130. Thus, when the disconnect clutch 126 is at least partially engaged, the torque converter 122 is connected to the engine 114. The torque converter 122 includes a pump wheel fixed to the M / G shaft 130 and a turbine fixed to the transmission input shaft 132. Thus, the torque converter 122 provides a hydrodynamic coupling between the shaft 130 and the transmission input shaft 132. The torque converter 122 transfers power from the pump wheel to the turbine when the pump wheel turns faster than the turbine. The magnitude of the turbine torque and the pump wheel torque generally depends on the relative rotational speeds. When the ratio of the pump wheel rotational speed to the turbine rotational speed is high enough, the turbine torque is a multiple of the pump wheel torque. The torque converter bypass clutch 134 can also be provided to frictionally or mechanically connect the pump wheel and turbine of the torque converter 122 when the torque converter bypass clutch 134 is engaged to allow more efficient power transfer. The torque converter bypass clutch 134 can also operate as a launch clutch to provide a smooth vehicle launch. Alternatively or in combination, for applications that do not include the torque converter 22 or the torque converter bypass clutch 134, a launch clutch similar to the disconnect clutch 126 can be provided between the M / G 118 and the gear box 124. In some applications, the disconnect clutch 126 is generally referred to as an upstream clutch and the launch clutch 134 (which can be a torque converter bypass clutch) is generally referred to as a downstream clutch.

[0017] The gear box 124 can include a gear set (not shown) that is selectively placed in different gear ratios by selectively engaging frictional elements such as clutches and brakes (not shown) to establish a desired number of discrete gear ratios or step ratios. The gear box 124 can provide a predetermined number of gear ratios that can range from a low gear (e.g., first gear) to a highest gear (e.g., Nth gear). A gear upshift of the gear box 124 is a shift to a higher gear. A gear downshift of the gear box 124 is a shift to a lower gear. The frictional elements can be controlled according to a shift schedule that sequentially connects and disconnects certain elements of the gear set to control the gear ratio between the transmission output shaft 136 and the transmission input shaft 132. The gear box 124 is automatically shifted from one gear ratio to another based on various vehicle operating conditions and environmental operating conditions by an associated controller 150, such as a powertrain control unit (PCU). The gear box 124 then provides a powertrain output torque to the output shaft 136.

[0018] It should be understood that the hydraulically controlled gearbox 124 used with the torque converter 122 is merely one example of a gearbox or transmission device; any multi-ratio gearbox that accepts input torque from an engine and / or motor and subsequently provides torque to an output shaft at different ratios is acceptable for use in embodiments of the present disclosure. For example, the gearbox 124 can be implemented by an automated mechanical (or manual) transmission (AMT) that includes one or more servo motors that translate / rotate a shift fork along a shift fork rail to select a desired gear ratio. As generally understood by one of ordinary skill in the art, an AMT can be used, for example, in applications having higher torque demands.

[0019] As shown in representative embodiments of the present disclosure, Figure 1 The output shaft 136 is connected to a differential 140, as shown in representative embodiments of the present disclosure. The differential 140 drives a pair of wheels 142 via respective axles 144 connected to the differential 140. The differential 140 transmits approximately equal torque to each wheel 142 while allowing for a slight difference in rotational speed, such as when the vehicle is turning. Different types of differentials or similar devices can be used to distribute torque from the powertrain to one or more wheels. For example, in some applications, the distribution of torque can be different depending on a particular mode of operation or condition.

[0020] The powertrain system 112 can also include an associated powertrain control unit (PCU) 150. While the PCU is shown as one controller, the PCU can be part of a larger control system and can be controlled by a number of other controllers in the overall vehicle 110, such as a vehicle system controller (VSC). Thus, it should be understood that the powertrain control unit 150, as well as one or more other controllers, can be collectively referred to as a "controller" that controls a number of actuators in response to signals from a number of sensors to control a number of functions, such as starting / stopping the engine 114, operating the M / G 118 to provide wheel torque or to charge the traction battery 120, selecting or scheduling transmission shifts, etc. The controller 150 can include a microprocessor or central processing unit (CPU) in communication with a number of types of computer readable storage devices or media. For example, the computer readable storage devices or media can include both volatile and nonvolatile memory in read-only memory (ROM), random access memory (RAM), and a non-failing memory (KAM). The KAM is a persistent or non-volatile memory that can be used to store various operating variables at power down of the CPU. The computer readable storage devices or media can be implemented using any of a number of known storage means, such as one of P ROM (programmable read only memory), EPROM (electrically programmable read only memory), EEPROM (electrically erasable programmable read only memory), flash memory or any other electrical, magnetic, optical, or combination storage devices capable of storing data, some of which represent executable instructions used by the controller to control the engine or vehicle.

[0021] The PCU 150 communicates with various engine / vehicle sensors and actuators via an input / output (I / O) interface, which can be implemented as a single integrated interface that provides various raw data or signal conditioning, processing and / or conversion, short circuit protection, etc. Alternatively, one or more dedicated hardware or firmware chips can be used to condition and process particular signals before passing them to the CPU. As in Figure 1Representative embodiments generally shown in FIG. 1, PCU 150 can communicate signals to and / or from engine 14, decoupling clutch 126, M / G 118, launch clutch 134, transmission gear box 124, and power electronics module 156. Although not explicitly shown, one of ordinary skill in the art will recognize the plurality of functions or components that can be controlled by PCU 150 within each of the aforementioned subsystems. Representative examples of parameters, systems, and / or components that can be actuated directly or indirectly using control logic executed by the controller include: fuel injection timing, rate, and duration, throttle position, spark plug ignition timing (for spark-ignition engines), intake / exhaust valve timing and duration, front end accessory drive (FEAD) components (such as air conditioning compressor), battery charging, regenerative braking, M / G operation, clutch pressure for decoupling clutch 126, launch clutch 134, and transmission gear box 124, etc. Sensors that communicate inputs through I / O interfaces can be used to indicate, for example: turbocharger boost pressure, crankshaft position (PIP), engine speed (RPM), wheel speed (WS1, WS2), vehicle speed (VSS), coolant temperature (ECT), intake manifold pressure (MAP), accelerator pedal position (PPS), ignition switch position (IGN), throttle position (TP), air temperature (TMP), exhaust gas oxygen (EGO) or other exhaust composition concentration or presence, mass air flow (MAF), transmission gear, ratio, or mode, transmission oil temperature (TOT), transmission turbine speed (TS), torque converter clutch 134 status (TCC), deceleration or shift mode (MDE).

[0022] The control logic or functions performed by PCU 150 may be represented by flowcharts or similar diagrams in one or more of the accompanying figures. These figures provide representative control strategies and / or logic that may be implemented using one or more processing strategies (such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc.). Therefore, the various steps or functions shown may be performed in the order shown, in parallel, or omitted in some cases. Although not always explicitly shown, those skilled in the art will recognize that one or more of the steps or functions shown may be repeated depending on the specific processing strategy used. Similarly, the order of processing is not necessarily required to achieve the functions and advantages described herein, but is provided for ease of illustration and description. The control logic may be primarily implemented in the form of software executed by a microprocessor-based vehicle, engine, and / or powertrain controller (such as PCU 150). Of course, the control logic may be implemented in the form of software, hardware, or a combination of software and hardware in one or more controllers, depending on the specific application. When implemented in software, the control logic may be provided in one or more computer-readable storage devices or media having stored thereon data representing code or instructions executed by a computer to control the vehicle or its subsystems. The computer-readable storage devices or media may include one or more of a number of known physical devices that utilize electronic, magnetic, and / or optical storage to store executable instructions and associated calibration information, operating variables, and the like.

[0023] The vehicle's driver uses an accelerator pedal 152 to provide the desired torque, power, or drive command to propel the vehicle. Generally speaking, depressing and releasing the accelerator pedal 152 generates an accelerator pedal position signal that the PCU 150 interprets as a request for increased or decreased power, respectively. Based at least on the input from the accelerator pedal, the PCU 150 commands torque from the engine 114 and / or the M / G 118. The PCU 150 also controls shift timing within the gearbox 124, as well as the engagement or disengagement of the disconnect clutch 126 and the torque converter bypass clutch 134. Similar to the disconnect clutch 126, the torque converter bypass clutch 134 can be adjusted within a range between engaged and disengaged positions. This adjustment also creates variable slip in the torque converter 122, in addition to the variable slip generated by the hydraulic coupling between the impeller and turbine. Alternatively, depending on the specific application, the torque converter bypass clutch 134 can be operated to lock up or disengage without using the modulating operating mode.

[0024] To utilize engine 114 to drive vehicle 110, at least partially engage decoupling clutch 126 to transmit at least a portion of engine torque through decoupling clutch 126 to M / G 118 and subsequently through torque converter 122 and gear box 124 from M / G 118. M / G 118 can assist engine 114 by providing additional power for turning shaft 130. This mode of operation can be referred to as "hybrid mode" or "electric assist mode."

[0025] To utilize M / G 118 as the sole source of power to drive vehicle 110, power flow remains unchanged except for operating decoupling clutch 126 to isolate engine 114 from the rest of powertrain 112. During this time, combustion in engine 114 can be disabled or otherwise turned off to conserve fuel. For example, traction battery 120 transmits stored electrical energy through high voltage (HV) bus 154 to power electronics module 156, which can include an inverter. High voltage bus 154 includes wiring and conductors for conducting current between modules, and can include positive side conductors and negative or return side conductors. Power electronics module 156 converts the DC voltage from traction battery 120 to an AC voltage used by M / G 118. Controller 150 commands power electronics module 156 to convert the voltage from traction battery 120 to an AC voltage provided to M / G 118 to provide positive or negative torque to shaft 130. This mode of operation can be referred to as "pure electric" mode of operation.

[0026] In any mode of operation, M / G 118 can be used as a motor and provide drive power to powertrain 112. Alternatively, M / G 118 can be used as a generator and convert kinetic energy from powertrain 112 into electrical energy to be supplied to high voltage bus 154 and / or stored in traction battery 120. For example, while engine 114 is providing propulsion power to vehicle 110, M / G 118 can be used as a generator. Also, during times of regenerative braking, M / G 118 can be used as a generator, where in regenerative braking, rotational energy from rotating wheels 142 is transferred back through gear box 124 and converted into electrical energy to be stored in traction battery 120.

[0027] It should be understood that, Figure 1The schematic diagram shown in FIG. 1 is merely exemplary and is not intended to be limiting. Other configurations utilizing selective engagement of both an engine and a motor to transmit torque through a transmission are contemplated. For example, the M / G 118 can be offset with respect to the crankshaft 128, additional motors can be provided to start the engine 114, and / or the M / G 118 can be disposed between the torque converter 122 and the gear box 124. Other configurations are contemplated without departing from the scope of the disclosure. Other hybrid vehicle configurations (e.g., power-split configurations) are possible and the inventive aspects disclosed herein can be applied to these other configurations.

[0028] The vehicle 110 can utilize the M / G 118 to start the engine 114. The controller 150 can command the disconnect clutch 126 to close and request torque from the M / G 118 via the power electronics module 156. The torque from the M / G 118 rotates the engine 114 such that the engine speed increases above a predetermined speed at which the engine 114 can be commanded to provide fuel and spark to maintain continuous engine rotation. The torque converter 122 can provide some torsional isolation during engine cranking and initial starting.

[0029] A low voltage starter system 168 can also be connected to the engine 114 to provide an auxiliary or backup means of starting the engine 114. The low voltage starter system 168 can be a belt integrated starter generator (BISG) system. An electric machine can be connected to the engine 114 by a belt guided through pulleys. The belt can be configured to connect the engine 114 and the electric machine such that they rotate together. In addition, there can be a clutch configured to engage and disengage the rotation of the electric machine. For example, the electric machine can be disengaged when the engine 114 does not need to be started or power is not needed. The electric machine can be configured to generate power when the belt is driven by engine power. The electric machine can be configured to drive the belt to rotate the engine crankshaft for starting the engine 114. The low voltage starter system 168 can include a control module that includes a power conversion system configured to transfer power between the electric machine and the vehicle power bus.

[0030] The vehicle 110 can also include a power converter module 158 and at least one auxiliary battery 160. The auxiliary battery 160 can be a low voltage battery, such as a 12 volt battery commonly used in motor vehicles. The terminals of the auxiliary battery 160 can be electrically connected to a low voltage power network or bus 166. The low voltage power network 166 includes wiring and conductors for conducting electrical current between connected modules. The power converter 158 can be electrically connected between the high voltage bus 154 and the low voltage power bus 166. The power converter 158 can be configured to transfer electrical power from the high voltage bus 154 to the low voltage power bus 166. The power converter 158 can be configured to convert high voltage power from the M / G 118 to low voltage power. For example, the high voltage power can be supplied at a voltage level compatible with the traction battery (e.g., 300 volts). The low voltage power can be supplied at a voltage level compatible with the auxiliary battery 160 (e.g., 12 volts). The power converter module 158 can be a DC / DC converter configured to convert the voltage from the high voltage bus 154 to a voltage level compatible with the low voltage power bus 166 (e.g., 12 volts). The power converter 158 can also be configured to convert the voltage from the low voltage power bus 166 to a voltage compatible with the high voltage bus 154. For example, the power converter 158 can be configured to provide bidirectional current flow between the high voltage bus 154 and the low voltage power bus 166 depending on the mode of operation.

[0031] The vehicle 110 can include a display. For example, the display can be part of an instrument panel. The display can include lights, illuminants, and / or other indicators for alerting an operator of conditions related to the vehicle. The display can be a liquid crystal display (LCD) module. The display can be in communication with a controller (e.g., the PCU 150) connected to the communication bus.

[0032] Figure 2 A feasible power distribution system 200 for a vehicle is depicted. The power distribution system 200 can include a power converter 158 connected between a high voltage bus 154 and a low voltage power network 166. The low voltage power network 166 can include a first low voltage bus 222 and a second low voltage bus 210. A disconnector 202 can be disposed between the first low voltage bus 222 and the second low voltage bus 210.

[0033] The power converter 158 can be characterized by a power limit. The power limit can identify a maximum amount of power that can be transferred by the power converter 158. The power limit can be a function of a rated power of a switching device and / or a current capability of a wiring within the power converter 158. The power limit can vary during operation of the power converter 158. For example, the power converter 158 can have a reduced power limit at higher temperatures. Reducing the power limit can prevent the power converter 158 from overheating during extreme operating conditions. The power converter 158 can increase and decrease the power limit based on operating conditions.

[0034] The first auxiliary battery 214 can be electrically connected to the first low voltage bus 222. The first set of electrical loads 224 can be electrically connected to the first low voltage bus 222 and receive power from the first low voltage bus 222 when activated.

[0035] The isolator 202 can include a switching element 206. The isolator 202 can include a diode (not shown) in parallel with the switching element 206. The switching element 206 can be a transistor (e.g., a metal oxide semiconductor field effect transistor (MOSFET)). The isolator 202 can be configured such that the switching element 206 is normally closed. In some configurations, the switching element 206 can be a relay. The switching element 206 can be configured such that current can flow between the first low voltage bus 222 and the second low voltage bus 210 when the switching element 206 is closed. The isolator 202 can be referred to as a vehicle power relay. The isolator 202 can be capable of isolating portions of the low voltage power network 166 from each other.

[0036] The second auxiliary battery 212 can be electrically connected to the second low voltage bus 210. The motor 226 of the low voltage starter system 168 (e.g., BISG) can be electrically connected to the second low voltage bus 210 using the second power converter module 204. The motor 226 can be configured to generate low voltage power when operating as a generator. The second power converter module 204 can be configured to convert the voltage from the motor 226 to a voltage compatible with the second low voltage bus 210. For example, the motor 226 can provide alternating current (AC) power to the second power converter module 204 when driven by the engine 114. The second power converter module 204 can be configured to convert the AC power to a direct current (DC) voltage / current (e.g., 12 volt DC voltage) compatible with the second low voltage bus 210. The second power converter module 204 can also be configured to provide voltage / current to the motor 226 that acts as a motor for starting the engine 114. The second power converter module 204 can include switching devices (e.g., solid state transistors, relays) configured to selectively connect the terminals of the motor 226 to the terminals of the second low voltage bus 210. Power transfer between the second low voltage bus 210 and the motor 226 can be achieved by operating the switching devices.

[0037] The second group of electrical loads 208 can be electrically connected to the second low voltage bus 210. The second group of electrical loads 208 can include a cooling fan for the engine 114.

[0038] The isolating switch 202 can be operated to be in a closed position such that the first low voltage bus 222 and the second low voltage bus 210 are electrically connected together and effectively function as a single low voltage bus or power network. In the following description, it can be assumed that the isolating switch 202 is in the closed position such that there is a single low voltage network.

[0039] The power distribution system 200 can include a controller 220. The controller 220 can communicate with components internal and external to the power distribution system 200. The controller 220 can include hardwired interfaces for communication and can include serial communication interfaces for communication via a vehicle communication network (e.g., controller area network). The controller 220 can communicate with the power converter 158 and the second power converter 204. The controller 220 can communicate with the PCU 150 associated with the engine 114. The controller 220 can also communicate with the first group of electrical loads 224 and the second group of electrical loads 208 connected to the first low voltage bus 222 and / or the second low voltage bus 210.

[0040] The operation of the electrical loads 224, 208 generates a power demand (e.g., a low voltage power demand) on the low voltage power network 166. The power demand of the low voltage power network 166 can be characterized by a peak power demand or a maximum total load power demand. The peak power demand can be the maximum possible power demand that can occur during vehicle operation. The peak power demand can occur during specific worst-case operating conditions.

[0041] The power demand on the low-voltage power network 166 can be met using power from the auxiliary battery 214 and / or the second auxiliary battery 212. The power demand can also be met using power provided by the power converter 158. Additionally, the power demand can be met using power from the second power converter 204, which is powered by the electric machine 226 driven by the engine 114.

[0042] Under normal operating conditions, it may be desirable to utilize power from the power converter 158 to support the low-voltage power network 166. Under these conditions, the power converter 158 may transfer energy from the high-voltage bus 154 to the low-voltage power network 166. The power converter 158 may be controlled to output an amount of power used to meet the power demands of the electrical loads 224, 208. Additionally, the power converter 158 may be controlled to output power used to charge the first auxiliary battery 214 and the second auxiliary battery 212. During normal load conditions, the power limit of the power converter 158 may be sufficient to meet the power demands on the low-voltage power network 166.

[0043] However, during some operating conditions, the power limit of power converter 158 may not be sufficient to meet the full power demand on low-voltage power network 166. During conditions where engine 114 operates under high load for extended periods, the power demand of electrical loads associated with engine cooling may increase. For example, the engine cooling fan may be activated to cool the engine coolant. The additional power demand from the engine cooling fan may cause the power demand on low-voltage power network 166 to exceed the power limit from power converter 158. In such conditions, the additional power demand may be met using power from first auxiliary battery 214 and / or second auxiliary battery 212. However, drawing power from auxiliary batteries 212 and 214 may reduce the respective state of charge of auxiliary batteries 212 and 214. It may be desirable to maintain auxiliary batteries 212 and 214 at a high state of charge so that battery power is available between ignition cycles.

[0044] Note that extreme power demands can occur only in rare circumstances. The power converter 158 can be designed to meet the extreme power demands, but the cost and size can be large. To reduce the cost and size of the power converter 158, it can be beneficial to design the power converter 158 for a power demand level that is less than the maximum possible low voltage power demand. By reducing the maximum power capacity of the power converter 158, other methods of meeting the maximum possible power demand can be implemented. The presence of the low voltage starter system 168, including the electric machine 226, allows for other options for meeting the power demand.

[0045] To prevent depletion of the auxiliary batteries 214 and 212 during high load conditions, it can be desirable to operate the electric machine 226 to generate power to the low voltage power network 166. In a typical high load condition, the engine 114 can be operating at an elevated rotational speed. The electric machine 226 can be controlled by the second power converter 204 to provide an amount of power to the low voltage power network 166. The sum of the power provided by the power converter 158 operating at a power limit and the power generation capability of the electric machine 226 can be at least equal to the maximum total load power demand of the low voltage power network 166.

[0046] The controller 220 can be configured to monitor the power demand of the low voltage power network 166. The power converter 158 can be configured to monitor the amount of power transferred from the high voltage network 154 to the low voltage power network 166. For example, the power converter 158 can include a current sensor and a voltage sensor at the output of the power converter 158. The power converter 158 can include a control module that monitors the voltage and current to derive the power output. The power value can be communicated to the controller 220. In other configurations, signals from the current sensor and the voltage sensor at the output of the power converter 158 can be routed to the controller 220. As described above, the power converter 158 can be characterized by a power limit. If the amount of power output by the power converter 158 is at or near the power limit, the controller 220 can determine that the power limit has been reached. In some configurations, a power value that is within a predetermined range of the power limit can indicate that the power limit has been reached. For example, an amount of power transferred that is more than 95% of the power limit can be determined to have reached the power limit. The predetermined range can allow for component tolerances of the power converter 158.

[0047] The power demand of the low voltage power network 166 can also be determined by monitoring the power flow to and from the auxiliary batteries 214 and 212. The first sensor unit 216 can be configured to measure the voltage and / or current of the first auxiliary battery 214. The second sensor unit 218 can be configured to measure the voltage and / or current of the second auxiliary battery 212. The sensor units 216 and 218 can include current sensors configured to measure the current to and from the associated battery. For example, the current sensors can be shunts or Hall effect sensors. The sensor units 216 and 218 can include voltage sensors configured to measure the voltage across the terminals of the associated battery. The voltage sensors can include circuitry configured to scale and filter the battery voltage to a level suitable for the inputs of the controller 220.

[0048] The power transmitted to or from the auxiliary batteries 212 and 214 can be calculated as the product of the associated voltage and current values. The power demand on the low voltage power network 166 can exceed the power limit of the power converter 158 when the power output of the power converter 158 has reached the power limit. The power demand can be determined to exceed the power limit when one or more of the auxiliary batteries 212 and 214 are delivering power to the low voltage power network 166 while the power converter 158 is operating at the power limit.

[0049] If the power demand of the low voltage power network 166 exceeds the power limit of the power converter 158, the controller 220 can operate the electric machine 226 to generate power to the low voltage power network 166 to meet the power demand. The power converter 158 can be operated at the power limit. The controller 220 can operate the electric machine 226 by controlling the operation of the second power converter 204 and the engine 114. The controller 220 can monitor the engine speed to determine whether the electric machine 226 will have sufficient power generation capability. If the engine 114 is currently stopped, the controller 220 can request that the engine 114 be started. The controller 220 can operate the second power converter 204 to operate the electric machine 226 as a motor to start the engine 114. Once the engine 114 is running, the controller 220 can request that the engine 114 run at a speed sufficient to generate the desired power output of the electric machine 226 and the second power converter 204 to meet the power demand.

[0050] If the power demand of the low voltage network 166 is less than or equal to the power limit of the power converter 158 and the power converter 158 is operable, the controller 220 can operate only the power converter 158 to meet the power demand. The power converter 158 can be operable when there are no conditions that prevent power transmission through the power converter 158.

[0051] The power output of the second power converter 204 can be controlled to be an amount of power that is the difference between the power demand and the power limit of the power converter 158. In some configurations, the power output can be controlled to be a predetermined amount of power. In other configurations, the power output of the second power converter 204 can be dynamically changed such that the power flowing into or out of the batteries 212 and 214 is less than a predetermined threshold.

[0052] In some conditions, the power converter 158 can be unable to transfer power from the high voltage bus 154. For example, the power converter 158 can be inoperable. For example, high temperature operation of the power converter 158 can cause internal switching devices to reach a critical temperature. To protect the switching devices, the switching devices can be shut down to prevent further degradation. The switching devices can be shut down until the temperature drops below a predetermined temperature. The power converter 158 can be permanently or temporarily unable to transfer power. In response to the power converter 158 being unable to transfer power between the high voltage bus 154 and the low voltage power network 166, the controller 220 can be configured to operate the electric machine 226 to generate power. The amount of generated power can be the lesser of the power demand of the low voltage power network 166 and the power limit of the electric machine 226.

[0053] The controller 220 can also be configured to operate the electric machine 226 to generate power in response to activation of a predetermined electrical load. The predetermined electrical load can include an infrequently used electrical load that is configured to request a high level of power demand. For example, the predetermined electrical load can include an engine cooling fan. It can be expected that the engine cooling fan can be activated during a heavy engine load that occurs infrequently.

[0054] Figure 3 A flowchart depicting a feasible sequence of operations for implementing a power distribution system is depicted. The operations can be implemented in a controller (e.g., the controller 220). At operation 302, inputs are collected and monitored. For example, status information can be received from the power converter 158, voltages and currents from sensors can be measured and stored. Information used to determine the power demand and the power limit can be received and / or calculated based on the received and measured inputs. The power converter 158 can be configured to transmit status information. For example, the power converter 158 can transmit any diagnostic codes that can result in the power converter 158 being unable to transfer power. Additionally, the power converter 158 can transmit any power limit information.

[0055] At operation 304, a check can be made to determine whether the power converter 158 is unable to transfer power. For example, in the event of a failure, the power converter 158 can be inoperable and the power converter 158 can send a diagnostic code or indicator indicating such a condition. If the power converter 158 is unable to transfer power, operation 314 can be performed.

[0056] If the power converter 158 is determined to be capable of power transfer, operation 306 can be performed. At operation 306, a power demand of the low voltage power network 166 can be determined. As described earlier herein, the power demand can be determined from voltage and current measurements. Additionally, the input can include status and operational information related to the electrical loads. At operation 308, a power limit of the power converter 158 can be determined. The power limit can be a stored value. The power limit can be a table of stored values indexed by an operating parameter (e.g., temperature). The power limit can be a value received from the power converter 158. At operation 310, the power demand is compared to the power limit. If the power demand is less than or equal to the power limit, operation 312 can be performed. At operation 312, the electric machine 226 can be operated normally. For example, the electric machine 226 can be normally idle. That is, the electric machine 226 can neither generate power nor operate as a motor. If the power demand is greater than the power limit, operation 314 can be performed.

[0057] At operation 314, the electric machine 226 can operate as a generator to generate power for the low voltage power network 166. The second power converter 204 can be controlled to convert the power generated by the electric machine 226 into a form compatible with the low voltage power network 166. At operation 316, the controller can manage the power output of the electric machine 226 by controlling the second power converter 204. For example, the electric machine 226 can be controlled to output an amount of power that is the difference between the power demand and the power limit. The power can be controlled by controlling the voltage and / or current supplied to the low voltage power network 166. At operation 318, the controller can manage the engine 114. Managing the engine 114 can include controlling the engine speed so that the electric machine 226 can generate a sufficient amount of power. Managing the engine 114 can also include starting the engine 114 if the engine 114 is in an off state.

[0058] The power generation operation of the electric machine 226 provides a number of benefits. The power converter 158 can be sized for a nominal power demand on the low voltage power network 166. The electric machine 226 and the second power converter 204 can supplement the power converter 158 during peak power demand. By sizing the power converter 158 for a nominal power demand rather than a peak power demand, the cost of the power converter 158 can be reduced. Additionally, the electric machine 226 and the second power converter 204 provide a secondary means of powering the low voltage power network 166 when the power converter 158 is unable to transfer power. For example, some power can be provided to the low voltage power network 166 in the event that the power converter 158 is inoperable. In such a case, the engine 114 can remain running to drive the electric machine 226.

[0059] The processes, methods, or algorithms disclosed herein can be embodied in hardware, software, firmware or any combination thereof. Such processes, methods, or algorithms can be implemented in any of the above-described control units, controllers, or computers, which can include any existing programmable electronic control unit or multiple existing programmable electronic control units working in concert. Similarly, the processes, methods, or algorithms can be stored as data and instructions on any computer-readable storage media for implementation by a controller or computer. Computer-readable storage media include any media that can be used to store various instructions as described above. Such media can include, but is not limited to, volatile memory, non-volatile memory, magnetic media, optical media, and the like. The software implementations of the processes, methods, or algorithms can be transmitted as generated data signals on a carrier wave or other signal that is generated by one of the above-described control units, controllers, or computers and that is transmitted to the other of the above-described control units, controllers, or computers. Similarly, software or programs can be transferred as generated data signals on a carrier wave or other signal on a bus that is coupled to the control units, controllers, or computers.

[0060] While the example embodiments have been described above, it is not intended that these embodiments describe all possible forms of the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, features of the various embodiments can be combined to form further embodiments of the present disclosure that are not expressly described or illustrated. While one or more embodiments have been described with reference to the preferred embodiment, it is understood that various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims, and their equivalents.

Claims

1. A vehicle comprising: a first electric machine configured to generate low voltage power; The controller is configured as: in response to a low-voltage power demand of an electrical load of the vehicle exceeding a limit of a power converter, operating a first electric machine and the power converter to meet the low-voltage power demand, the power converter being configured to convert high-voltage power generated by a second electric machine into low-voltage power, and in response to the low-voltage power demand exceeding the limit and an engine connected to the first electric machine being stopped, operating the first electric machine to start the engine; In response to the power converter being operational, if the low-voltage power demand does not exceed a limit of the power converter, the power converter is only operated to meet the low-voltage power demand.

2. The vehicle according to claim 1, wherein The controller is further configured to operate the first electric machine to produce an amount of power that is a difference between the low-voltage power demand and the limit.

3. The vehicle according to claim 1, wherein The controller is further configured to operate an engine coupled to the first electric machine at at least a predetermined speed configured to cause the first electric machine to generate an amount of power that satisfies the low-voltage power demand.

4. The vehicle according to claim 1, wherein The sum of the limit and the power capacity of the first electric machine is at least equal to the maximum possible low-voltage power.

5. The vehicle according to claim 1, wherein The limit is less than the maximum possible low voltage power requirement.

6. A method for low voltage power distribution, comprising: converting high voltage power generated by the first electric machine into low voltage power via a power converter; operating the power converter and a second electric machine in response to a low-voltage power demand of an electric load of the vehicle exceeding a limit of the power converter, wherein the second electric machine is configured to generate low-voltage power, and operating the second electric machine to start the engine in response to the low-voltage power demand exceeding the limit and an engine connected to the second electric machine being stopped; In response to the power converter being operational, if the low-voltage power demand does not exceed a limit of the power converter, the power converter is only operated to meet the low-voltage power demand.

7. The method according to claim 6, further comprising: In response to the power converter being unable to convert the high-voltage power to the low-voltage power, only the second electric machine is operated to generate the low-voltage power.

8. The method according to claim 7, wherein: The amount of power produced by the second electric machine is the lesser of the low voltage power demand and a power limit of the second electric machine.

9. The method according to claim 7, further comprising: An engine coupled to the second electric machine is operated at at least a predetermined speed configured to cause the second electric machine to generate an amount of low-voltage power that satisfies the low-voltage power demand.

10. The method according to claim 7, further comprising: In response to an engine connected to the second electric machine being stopped, the engine is started.

11. The method according to claim 6, wherein: The limit is less than the maximum possible low voltage power requirement.

12. A vehicle comprising: a first electric machine configured to generate low voltage power; a power converter configured to convert high-voltage power generated by the second electric machine into low-voltage power; a controller configured to: in response to the power converter being unable to convert the high-voltage power to the low-voltage power, operate only the first electric machine to generate an amount of power that satisfies a low-voltage power demand of an electrical load of the vehicle; In response to the low-voltage power demand exceeding a limit of the power converter, operating the first electric machine and the power converter to meet the low-voltage power demand, and in response to the low-voltage power demand exceeding the limit and an engine connected to the first electric machine being stopped, operating the first electric machine to start the engine.

13. The vehicle according to claim 12, wherein: The controller is further configured to operate the first electric machine to generate an amount of power that is lesser of the low voltage power demand and a power limit of the first electric machine.

14. The vehicle according to claim 12, wherein: Operating only the first electric machine includes operating an engine configured to drive the first electric machine at at least a predetermined speed configured to cause the first electric machine to generate the amount of power.

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