Vehicle electrical system with isolation circuit

An electrical system for a vehicle includes a DC/DC converter electrically connected to a high-voltage power source and a first bus, a second bus electrically connected to a second low-voltage power source, and an isolation circuit electrically connected to the first and second buses. The isolation circuit permits current flow in only one direction from the first bus to the second bus.

BACKGROUND

Hybrid-electric, electric, and conventional (internal-combustion engine) vehicles typically include a power system for supplying power to various loads. The power system typically includes a low-voltage battery, e.g., 12 or 48 volts, which can supply energy to the loads. In a hybrid-electric vehicle, the power system includes a DC/DC converter that supplies power to the loads unless the power demanded by the loads exceeds the capacity of the DC/DC converter, in which case the low-voltage battery supplies the loads.

DETAILED DESCRIPTION

An electrical system for a vehicle includes a DC/DC converter electrically connected to a high-voltage power source and a first bus, a second bus electrically connected to a low-voltage power source, and an isolation circuit electrically connected to the first and second buses. The isolation circuit permits current flow in only one direction from the first bus to the second bus.

The isolation circuit may include a diode including a cathode and an anode electrically connected to the first bus.

The isolation circuit may be a diode including an anode electrically connected to the first bus, and a cathode electrically connected to the second bus.

The isolation circuit may include a switch electrically connecting the first and second buses, and the switch may be configured to open when one of the first and second buses is short-circuited. The switch may be a relay including a control lead electrically connected to the one of the first and second buses. The electrical system may further include a diode electrically connecting the control lead and the one of the first and second buses.

The switch may be a first switch configured to open when the first bus is short-circuited, the electrical system may further include a second switch electrically connecting the first and second buses, and the second switch may be configured to open when the second bus is short-circuited. The first switch may be a first relay including a first control lead electrically connected to the first bus, and the second switch may be a second relay including a second control lead electrically connected to the second bus. The electrical system may further include a first diode electrically connecting the first control lead and the first bus, and a second diode electrically connecting the second control lead and the second bus.

The first and second switches may be arranged in series between the first and second buses.

The low-voltage power source may be a second low-voltage power source, and the electrical system may further include a first low-voltage power source electrically connected to the first bus.

The electrical system may further include a plurality of loads electrically connected to the first bus.

The electrical system may further include a plurality of loads electrically connected to the second bus. The loads may include a contactor for the high-voltage power source. The contactor may electrically connect the high-voltage power source to the first bus. The loads may include a control module programmed to operate the contactor.

An electrical system for a vehicle includes a DC/DC converter electrically connected to a high-voltage power source and a first bus, a second bus electrically connected to a low-voltage power source and the first bus, and means for isolating the second bus from the first bus in response to the first bus short-circuiting.

The electrical system may further include means for isolating the second bus from the first bus in response to the second bus short-circuiting.

An electrical system30for a vehicle32includes a first DC/DC converter34electrically connected to a high-voltage power source36and a first bus38, a second bus40electrically connected to a second low-voltage power source42, and an isolation circuit44electrically connected to the first and second buses38,40. (The adjectives “first” and “second” are used throughout this document as identifiers and are not intended to signify importance or order.) The isolation circuit44permits current flow in only one direction from the first bus38to the second bus40.

The electrical system30provides improved reliability for the vehicle32. In the event that the first bus38experiences a short circuit, the second bus40can still be supplied with power by the second low-voltage power source42. Whatever systems are connected to the second bus40can thus continue to operate even after an electrical failure. The vehicle32may be able to perform, e.g., a minimal risk condition even after an electrical failure instead of possibly becoming immediately disabled. For purposes of this disclosure, that term has the meaning accorded by the National Highway Traffic Safety Administration (NHTSA) and the Society of Automotive Engineers (SAE): “‘Minimal risk condition’ means low-risk operating condition that an automated driving system automatically resorts to either when a system fails or when the human driver fails to respond appropriately to a request to take over the dynamic driving task.” (U.S. Dept. of Transportation & NHTSA,Automated Driving Systems2.0:A Vision for Safety,at 26 (citing SAE International J3016, International Taxonomy and Definitions for Terms Related to Driving Automation Systems for On-Road Motor Vehicles (J3016:Sept2016)).) For example, the minimal risk condition may specify initiating a handover to the human driver or autonomously driving the vehicle32to a halt at a roadside, i.e., stopping the vehicle32outside active lanes of traffic.

With reference toFIG. 1, the vehicle32may be an autonomous or semi-autonomous vehicle. A vehicle computer can be programmed to operate the vehicle32independently of the intervention of a human driver, completely or to a lesser degree. The vehicle computer may be programmed to operate a propulsion46, brake system, steering system, and/or other vehicle systems. For the purposes of this disclosure, autonomous operation means the vehicle computer controls the propulsion46, brake system, and steering system without input from a human driver; semi-autonomous operation means the vehicle computer controls one or two of the propulsion46, brake system, and steering system and a human driver controls the remainder; and nonautonomous operation means a human driver controls the propulsion46, brake system, and steering system.

The propulsion46of the vehicle32generates energy and translates the energy into motion of the vehicle32. In particular, the propulsion46may be hybrid propulsion. The propulsion46may include a powertrain48in any hybrid arrangement, e.g., a series-hybrid powertrain (as shown inFIG. 1), a parallel-hybrid powertrain, a power-split (series-parallel) hybrid powertrain, etc. The propulsion46can include an electronic control unit (ECU) or the like that is in communication with and receives input from the vehicle computer and/or a human driver, e.g., a hybrid-powertrain control module50. The human driver may control the propulsion46via, e.g., an accelerator pedal and/or a gear-shift lever.

The propulsion46includes the powertrain48that transmits power from an engine52, from the high-voltage power source36, or from both the engine52and the high-voltage power source36, to a transmission54and ultimately to wheels56of the vehicle32. The engine52is an internal-combustion engine and may contain cylinders that serve as combustion chambers that convert fuel from a reservoir58to rotational kinetic energy. A generator60may receive the rotational kinetic energy from the engine52. The generator60converts the rotational kinetic energy into electricity, e.g., alternating current, and powers an electric motor62. A charger/inverter64may convert the output of the generator60, e.g., the alternating current, into high-voltage direct current to supply the high-voltage power source36. For the purposes of this disclosure, “high voltage” is defined as at least 60 volts direct current or at least 30 volts alternating current. For example, the high-voltage direct current may be on the order of 400 volts. The charger/inverter64controls how much power is supplied from the high-voltage power source36to the generator60of the powertrain48. The electric motor62may convert the electricity from the generator60into rotational kinetic energy transmitted to the transmission54. The transmission54transmits the kinetic energy via, e.g., a drive axle to the wheels56, while applying a gear ratio allowing different tradeoffs between torque and rotational speed.

The high-voltage power source36produces a voltage of at least 60 volts direct current, e.g., on the order of 400 volts direct current. The high-voltage power source36may be any type suitable for providing high-voltage electricity for operating the vehicle32, e.g., a battery such as lithium-ion or lead-acid, a capacitor, etc. The high-voltage power source36is electrically coupled to the powertrain48via the charger/inverter64.

With reference toFIGS. 2-4, the vehicle32includes a plurality of control modules50,66,68,70,72,74. The control modules50,66,68,70,72,74may include the hybrid-powertrain control module50, a battery-energy control module66, a body control module68, an antilock brake control module70, a first power-steering control module72, and a collision-mitigation-system control module74, as shown inFIGS. 3 and 4. The control modules50,66,68,70,72,74may be microprocessor-based computers. Each control module50,66,68,70,72,74includes memory, at least one processor, etc. The memories of the control modules50,66,68,70,72,74include memory for storing instructions executable by the processors as well as for electronically storing data and/or databases.

With reference toFIG. 2, a contactor76is positioned to control the supply of electricity from the high-voltage power source36to the first DC/DC converter34and a second DC/DC converter82. The contactor76is an electrically controlled switch. The contactor76includes a switch78and a coil80, or electromagnet, for controlling the switch78. Alternatively, the contactor76may include a solid-state circuit for controlling the switch78. The contactor76may be normally open; i.e., the switch78is open when current is not flowing through the coil80or solid-state circuit.

The contactor76may be operated by, e.g., the hybrid-powertrain control module50and/or the battery-energy control module66; in other words, the hybrid-powertrain control module50and/or the battery-energy control module66may transmit current through the coil80or solid-state circuit to close the switch78of the contactor76. The hybrid-powertrain control module50and/or the battery-energy control module66may be programmed to operate the contactor76, e.g., conditions for opening and closing the contactor76.

For example, the hybrid-powertrain control module50may operate the contactor76, and the battery-energy control module66may include two BECM relays84controlled by the contactor76. Each BECM relay may supply current from the high-voltage power source36to one of the first DC/DC converter34and the second DC/DC converter82when closed. The BECM relays84may be electrically controlled switches, e.g., by a coil or solid-state circuit. The BECM relays84may be normally open. The contactor76may be connected to supply current to the coil or solid-state circuit of the BECM relays84when closed. When the contactor76is closed, current flows from the contactor76through the coil or solid-state circuit of the BECM relays84to low-side drivers85, closing the BECM relays84and supplying current from the high-voltage power source36to the DC/DC converters34,82.

The first DC/DC converter34is positioned to receive current from the high-voltage power source36and deliver current to a first power-distribution board90, specifically, to the first bus38(as shown inFIGS. 3 and 4). The second DC/DC converter82is positioned to receive current from the high-voltage power source36and deliver current to a third low-voltage power source86and a second power-distribution board91, which distributes the current to third loads88. The DC/DC converters34,82may receive high-voltage direct current from the charger/inverter64and/or the high-voltage power source36and convert the high-voltage direct current to low-voltage direct current. For the purposes of this disclosure, “low voltage” is defined as less than 60 volts direct current or less than 30 volts alternating current. For example, the low-voltage direct current may be 12 volts or 48 volts. The first DC/DC converter34may exchange the low-voltage direct current with a first low-voltage power source92, and the first DC/DC converter34may supply the low-voltage direct current to the first bus38.

With reference toFIGS. 3 and 4, the first power-distribution board90divides current into subsidiary circuits, i.e., a plurality of loads94,96. The first power-distribution board90includes the first bus38, the second bus40, and one or more fuses98. The loads94,96include first loads94electrically connected to the first bus38and second loads96electrically connected to the second bus40. Current from the first DC/DC converter34and/or from the first low-voltage power source92flows to the first bus38and then either to the second bus40via the isolation circuit44or to the first loads94. Current flows from the second bus40to the second loads96. The first loads94may include the antilock brake control module70, the first power-steering control module72, the collision-mitigation-system control module74, an air-conditioning system100, a fan102for cooling the engine52, a blower motor104, other high-current loads106, and other nonsafety loads110. The high-current loads106are defined for the purposes of this disclosure as loads with a fuse rating above 30 amperes. The second loads96may include the battery-energy control module66, the hybrid-powertrain control module50, the body control module68, and the contactor76.

The low-voltage power sources42,86,92each produces a voltage less than 60 volts direct current, e.g., 12 or 48 volts direct current. The low-voltage power sources42,86,92may be any type suitable for providing low-voltage electricity for power the loads88,94,96, e.g., batteries such as lithium-ion or lead-acid, capacitors, etc. For example, as shown inFIGS. 3 and 4, the first low-voltage power source92is a lead-acid battery, and the second low-voltage power source42is a lithium-ion battery. The first low-voltage power source92is electrically connected to the first bus38, and the second low-voltage power source42is electrically connected to the second bus40.

In normal operation, i.e., the electrical system30has not experienced any short circuits, the first and second loads94,96are typically powered via the first DC/DC converter34without drawing power from the first low-voltage power source92. The first low-voltage power source92can supply power in the event of transient demands from the first and second loads94,96for greater power than the first DC/DC converter34can supply.

With continued reference toFIGS. 3 and 4, the isolation circuit44is electrically connected to the first and second buses38,40. The isolation circuit44permits current to flow in only one direction from the first bus38to the second bus40. Current cannot flow through the isolation circuit44from the second bus40to the first bus38. The isolation circuit44isolates the second bus40from the first bus38in response to the first bus38short-circuiting. For example, as shown inFIG. 3, the isolation circuit44may be a diode112. For another example, as shown inFIG. 4, the isolation circuit44may include a first switch114configured to open, e.g., as described in more detail below, when the first bus38is short-circuited. For another example, the isolation circuit44may include a controller (not shown) programmed to, in response to receiving data indicating that the first bus38is short-circuited, instruct a switch connecting the first and second buses38,40to open.

If the first bus38short-circuits and the isolation circuit44isolates the second bus40from the first bus38, then current from the second low-voltage power source42flows through the second bus40to the second loads96. The hybrid-powertrain control module50, the battery-energy control module66, and the contactor76are thus able to continue operating even when the first bus38short-circuits. Because the contactor76continues to operate, the high-voltage power source36can still supply power to the second DC/DC converter82.

The isolation circuit44may also isolate the second bus40from the first bus38in response to the second bus40short-circuiting. For example, as shown inFIG. 4, the isolation circuit44may include a second switch116configured to open when the second bus40is short-circuited. For another example, the isolation circuit44may include a controller (not shown) programmed to, in response to receiving data indicating that the second bus40is short-circuited, instruct a switch connecting the first and second buses38,40to open.

If the second bus40short-circuits and the isolation circuit44isolates the second bus40from the first bus38, the first bus38is still able to support the first loads94with current from the first DC/DC converter34and/or the first low-voltage power source92.

With reference toFIG. 3, the isolation circuit44may include the diode112. For example, the isolation circuit44may be the diode112. The diode112includes a cathode118and an anode120. For the purposes of this disclosure, a “diode” is defined as a two-terminal electrical component that conducts current primarily in one direction from the anode to the cathode. For example, the diode112may have very low resistance in the direction from the anode120to the cathode118and very high resistance in the direction from the cathode118to the anode120. The diode112may be any suitable type, e.g., point-contact diode, solid-state diode, semiconductor diode, etc. The anode120is electrically connected to the first bus38. The cathode118is electrically connected to the second bus40. Current can thus flow from the first bus38to the second bus40but not from the second bus40to the first bus38; therefore, if the first bus38short-circuits, current does not flow from the first bus38to the second bus40despite the second bus40being at a higher voltage than the first bus38.

With reference toFIG. 4, the isolation circuit44may include the first switch114and the second switch116. The first switch114is configured to open when the first bus38is short-circuited. For example, the first switch114may be a first relay, i.e., an electrically controlled switch. The first switch114includes a switch122and a coil124, or electromagnet, for controlling the switch122. Alternatively, the first switch114may include a solid-state circuit for controlling the switch122. The first switch114may be normally open, i.e., open when current is not flowing through the coil124or solid-state circuit, or normally closed, i.e., closed when current is not flowing through the coil124or solid-state circuit. As shown inFIG. 4, the first switch114is normally open.

The first switch114may include a control lead126electrically connected to the first bus38and a control lead126electrically connected to ground. For the purposes of this disclosure, a “control lead” is defined as a lead from the coil or solid-state circuit of a relay. The control lead126may be electrically connected to the first bus38via a first diode128. The first diode128may be arranged to permit current to flow from but not to the first bus38, i.e., with the anode electrically connected to the first bus38and the cathode to the control lead126. The first switch114may include a switch lead130electrically connected to the first bus38and a switch lead130electrically connected to the second bus40via the second switch116. For the purposes of this disclosure, a “switch lead” is defined as a lead from the switch of a relay.

When the first bus38has a positive voltage, i.e., is not short-circuited, current flows through the first diode128and coil124to ground. The current flowing through the coil124causes the switch122of the first switch114to remain closed, so current can flow through the switch122from the first bus38to the second bus40. When the first bus38short-circuits, the amount of current flowing through the first diode128and the coil124is zero or negligibly close to zero. With no current flowing through the coil124, the switch122opens, preventing current from flowing between the first bus38and the second bus40.

The second switch116is configured to open when the second bus40is short-circuited. For example, the second switch116may be a second relay, i.e., an electrically controlled switch. The second switch116includes a switch132and a coil134, or electromagnet, for controlling the switch132. Alternatively, the second switch116may include a solid-state circuit for controlling the switch132. The second switch116may be normally open, i.e., open when current is not flowing through the coil134or solid-state circuit, or normally closed, i.e., closed when current is not flowing through the coil134or solid-state circuit.

The second switch116may include a control lead136electrically connected to the second bus40and a control lead136electrically connected to ground. The control lead136may be electrically connected to the second bus40via a second diode138. The second diode138may be arranged to permit current to flow from but not to the second bus40, i.e., with the anode electrically connected to the second bus40and the cathode to the control lead136. The second switch116may include a switch lead140electrically connected to the second bus40and a switch lead140electrically connected to the first bus38via the first switch114. In other words, the first switch114and the second switch116are arranged in series. Both the first switch114and the second switch116must be closed for current to flow between the first bus38and the second bus40.

When the second bus40has a positive voltage, i.e., is not short-circuited, current flows through the second diode138and coil134to ground. The current flowing through the coil134causes the switch132of the second switch116to remain closed, so current can flow through the switch132from the first bus38to the second bus40. When the second bus40short-circuits, the amount of current flowing through the second diode138and the coil134is zero or negligibly close to zero. With no current flowing through the coil134, the switch132opens, preventing current from flowing between the first bus38and the second bus40.