Method and apparatus for starting an internal combustion engine

A starting system for an internal combustion engine includes a starter motor configured to transfer torque to the engine during an engine starting event, a low-voltage power bus including a first bus segment and a second bus segment, a controllable isolation circuit including a first state wherein the first and second bus segments are electrically coupled and a second state wherein the first and second bus segments are electrically isolated, a low-voltage battery and the starter motor electrically coupled to the first bus segment, an accessory power module and a power supply for a control module electrically coupled to the second bus segment; and the control module configured to control the isolation circuit to the second state to electrically isolate the first bus segment from the second bus segment during the engine starting event.

TECHNICAL FIELD

This disclosure is related to starting systems for internal combustion engines.

BACKGROUND

Vehicle electrical systems including electric machines, e.g., motors and accessory drive devices that receive electric power from energy storage devices, e.g., batteries, and are controlled by signals originating from control modules and other control devices and logic circuits. One electric circuit includes an electric-powered starter motor that spins an internal combustion engine when activated with an ignition switch. Control modules are electrically powered and functional to operate as intended only when electric power is greater than a minimum operating voltage for integrated circuits and other components thereof, e.g., 5V DC.

During an engine starting event, power draw by a starter motor can cause battery voltage and system voltage to fall below a minimum operating voltage of the integrated circuits of the control modules, thus affecting their ability to function. A known method for maintaining system voltage greater than a minimum operating voltage is to include a boost electric power supply in a control module, resulting in increased control module circuit complexity and associated cost.

In a hybrid vehicle system using an internal combustion engine in conjunction with electric torque machines to generate tractive torque, an auxiliary or accessory power module can be used in place of an alternator/generator to support low-voltage loads and electrically charge a low-voltage battery. The auxiliary power module converts energy from the high-voltage hybrid battery system to low-voltage to support the low-voltage system. A peak power rating for an auxiliary power module configured to provide electric power to a starter motor must be sufficient to operate the starter motor across a wide range of ambient conditions, engine operating conditions and associated electric loads. An auxiliary power module having sufficient electric power capacity to operate a starter motor may not be cost-effective.

SUMMARY

A starting system for an internal combustion engine includes a starter motor configured to transfer torque to the engine during an engine starting event, a low-voltage power bus including a first bus segment and a second bus segment, a controllable isolation circuit including a first state wherein the first and second bus segments are electrically coupled and a second state wherein the first and second bus segments are electrically isolated, a low-voltage battery and the starter motor electrically coupled to the first bus segment, an accessory power module and a power supply for a control module electrically coupled to the second bus segment; and the control module configured to control the isolation circuit to the second state to electrically isolate the first bus segment from the second bus segment during the engine starting event.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,FIG. 1schematically shows a vehicle10including a control system100, a hybrid powertrain system200, and a driveline300. Like numerals refer to like elements in the description.

The driveline300can include a differential gear device310that mechanically couples to an axle320or half-shaft that mechanically couples to a wheel330in one embodiment. The differential gear device310is coupled to an output member64of the hybrid powertrain system200, and transfers output power therebetween. The driveline300transfers tractive power between the hybrid powertrain system200and a road surface.

The hybrid powertrain system200includes an internal combustion engine240and torque machine(s)230that are mechanically coupled to a hybrid transmission250. Mechanical power originating in the engine240can be transferred to the output member64and the torque machine(s)230via an input member12and using the hybrid transmission250. Parameters associated with such input power from the engine240include input torque TEand input speed NE. Mechanical power from the torque machine(s)230can be transferred to the output member64and the engine240using the hybrid transmission250. Parameters associated with such mechanical power transfer include motor torque TMand motor speed NM. Mechanical power can be transferred between the hybrid transmission250and the driveline300via the output member64. Parameters associated with such mechanical power transfer include output torque TOand output speed NO.

Preferably, the engine240is a multi-cylinder internal combustion engine selectively operative in a plurality of states, including one of an engine-on state and an engine-off state, one of an all-cylinder state and a cylinder deactivation state, and one of a fueled state and a fuel cutoff state. In one embodiment, the hybrid transmission250is operative in one of a plurality of range states including fixed gear and continuously variable range states through selective activation of one or more torque transfer clutches. In one embodiment, the engine240is a spark-ignition engine with timing of combustion controlled by advancing or retarding spark ignition timing. Alternatively, the engine240is a compression-ignition engine with timing of combustion controlled by advancing or retarding timing of fuel injection events. It is appreciated that the engine240can be configured to operate in other combustion modes.

It is appreciated that the hybrid transmission250can be configured and controlled to transfer mechanical power therethrough using one or more differential gear sets and selective activation of one or more torque transfer devices, e.g., clutches, in one embodiment.

The torque machine(s)230, engine240and hybrid transmission250each include a plurality of sensing devices for monitoring operation thereof including rotational position sensors, e.g., resolvers, for monitoring rotational position and speed of each of the torque machine(s)230. The torque machine(s)230, engine240and hybrid transmission250include a plurality of actuators for controlling operation thereof. The engine240includes a starter motor (Starter)245. The starter motor245is preferably a solenoid-controlled low-voltage electric motor configured to generate rotational torque to spin the engine240in response to an activation signal originating from the control system100.

A high-voltage energy storage device (HV Batt)210stores potential energy and is coupled via a high-voltage power bus165and controllable power inverter(s) to one or more torque machine(s)230to transfer power therebetween. Preferably the high-voltage energy storage device210includes an electrical storage device that can include a plurality of electrical cells, ultracapacitors, and other devices configured to store electric energy on-vehicle. The torque machine(s)230preferably include multi-phase electric motor/generators configured to convert stored electric energy to mechanical power and convert mechanical power to electric energy that can be stored in the high-voltage battery210through the controllable power inverter(s) in response to control signals originating from the control system100. The engine240converts fuel stored in a fuel tank to mechanical power through a combustion process.

The control system100includes a control module120that is signally connected to an operator interface130. The control module120includes a low-voltage electric power supply122to provide regulated low-voltage electric power thereto. The operator interface130preferably includes a plurality of human/machine interface devices through which an operator commands operation of the vehicle10, including an ignition switch, an accelerator pedal, a brake pedal, and a transmission range selector (PRNDL). Although the control module120and operator interface130are shown as discrete elements, such an illustration is for ease of description. It should be recognized that the functions described as being performed by the control module120may be combined into one or more devices, e.g., implemented in software, hardware, and/or application-specific integrated circuitry (ASIC) and ancillary circuits that may be separate and distinct from the control module120. The control module120preferably includes one or more general-purpose digital controllers, each including a microprocessor or central processing unit, storage mediums including read only memory (ROM), random access memory (RAM), electrically programmable read only memory (EPROM), a high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, and input/output circuitry and devices (I/O) and appropriate signal conditioning and buffer circuitry. The control module120has a set of control algorithms, including resident program instructions and calibrations stored in one of the storage mediums and executed to provide respective functions. The control module120is shown signally connected to a communications bus175for information transfer. It is appreciated that information transfer to and from the control module120can be accomplished by one or more communications paths, including using a direct connection, using a local area network bus and using a serial peripheral interface bus. The algorithms of the control schemes are executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices are executed by the central processing unit to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of actuators associated with elements of the hybrid powertrain system200using calibrations. Loop cycles are executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing operation of the hybrid powertrain. Alternatively, algorithms may be executed in response to the occurrence of an event.

The control module120preferably signally and operatively connects to individual elements of the hybrid powertrain system200via the communications bus175. The control module120signally connects to the sensing devices of each of the torque machine(s)230, the engine240, and the hybrid transmission250to monitor operation and determine parametric states thereof. Monitored states of the engine240preferably include engine speed (NE), engine torque (TE) or load, and temperature. Monitored states of the hybrid transmission250preferably include rotational speed, and hydraulic pressure at a plurality of locations, from which parametric states including application of specific torque transfer clutches can be determined. Monitored states of the torque machine(s)230preferably include speed(s) (NM) and power flow(s), e.g., electric current flow, from which a parametric state for motor torque(s) (TM) output from the torque machine(s)230can be determined.

The control module120operatively connects to the actuators of each of the torque machine(s)230, the engine240, and the hybrid transmission250to control operation thereof in accordance with executed control schemes that are stored in the form of algorithms and calibrations. The actuators associated with the torque machine(s)230preferably include the controllable power inverter(s). The actuators associated with the engine240preferably include the starter motor245and other actuators, e.g., fuel injectors, air flow controllers, spark ignition systems, and other known devices associated with controlling engine operation including controlling engine states. The actuators associated with the hybrid transmission250include solenoid devices for actuating torque transfer clutches to effect operation in specific range states.

The vehicle10includes a low-voltage power bus155for transferring low-voltage DC electric power within the vehicle10. The low-voltage DC electric power has a voltage range of 12-14V DC in one embodiment. The low-voltage power bus155includes a first bus segment155A and a second bus segment155B, which are selectively coupled via an isolation circuit (Iso Circuit)160. An accessory power module (APM)225and the low-voltage electric power supply122electrically connect to the second bus segment155B. A low-voltage battery device (LV Batt)235electrically connects to the first bus segment155A. The starter motor245is configured to electrically connect to the first bus segment155A to draw electric current from the low-voltage battery235to generate rotational torque to spin the engine240in response to the aforementioned control signal to start the engine240originating from the control system100.

The accessory power module (APM)225electrically connects to the high-voltage energy storage device (HV Batt)210via a high-voltage power bus165. The accessory power module225is an electric power converter that steps down a portion of the high-voltage DC electric power available on the high-voltage power bus165to low-voltage DC electric power, preferably in the 12-14V DC range, to provide electric power to low-voltage on-vehicle electrically-powered accessories. The accessory power module (APM)225electrically connects to the low-voltage electric power supply122.

FIG. 2schematically shows an electrical circuit including the low-voltage power bus155including the first bus segment155A and the second bus segment155B with the isolation circuit160. The low-voltage power bus155electrically connects the low-voltage battery device235, the starter motor (Starter)245, and the accessory power module (APM)225, and transfers electric power to the low-voltage electric power supply122of the control module120. The control module120connects to the starter motor245and the isolation circuit160via the communications bus175to control operation thereof.

The isolation circuit160includes an isolation switch device164wired in parallel with an isolation diode162in one embodiment. The isolation circuit160is controlled to permit the low-voltage power bus155to supply low-voltage electric power from the low-voltage battery device235to the second bus segment155B without active control by the control module120. The isolation switch device164is controllable to one of an open state, as shown, and a closed state, and is preferably operatively controlled by a signal output from the control module120. In one embodiment, the isolation switch device164is an IGBT device. When the isolation switch device164is an IGBT device, the IGBT device may include an internal diode that renders the isolation diode162redundant and thus is omitted. Alternatively, the isolation switch device164is a normally-closed electromechanical relay device that is controlled to an open state by a control signal from the control module120to isolate the first bus segment155A from the second bus segment155B prior to engaging the starter motor245to start the engine240. It is appreciated that the isolation switch device164can include other hardware configurations.

The isolation diode162is oriented with a forward bias from the low-voltage battery235to the accessory power module225, including an anode (+) oriented towards the low-voltage battery235and a cathode (−) oriented towards the accessory power module225. When the isolation switch device164is in the open state, electric current can flow from the low-voltage battery235to the accessory power module225via the first bus segment155A through the isolation diode162and the second bus segment155B. Furthermore, electric current can flow from the low-voltage battery235to the starter motor245, and electric current can flow from the accessory power module225to the low-voltage electric power supply122of the control module120and to other accessories. The presence and operation of the isolation diode162prevents electric current from flowing from the second bus segment155B to the first bus segment155A, including preventing electric current from flowing from the accessory power module225to the low-voltage battery235and the starter motor245when the isolation switch device164is in the open state. When the isolation switch device164is in the closed state, electric current can flow in either direction between the first bus segment155A and the second bus segment155B. Thus, electric current can flow between the low-voltage battery235, the starter motor245, the accessory power module225, the low-voltage electric power supply122of the control module120and other accessories.

Operation of the aforementioned system in the hybrid vehicle10is described with reference to Table 1.

In operation, the control module120controls the isolation switch device164as follows. When the vehicle is in an off state (Vehicle Off), a vehicle ignition switch is off (OFF) and the isolation switch device164is in the open state (OPEN). The low-voltage battery235supplies required electric current to the accessory power module225and the low-voltage electric power supply122of the control module120through the low-voltage power bus155via the isolation diode162.

When the operator indicates an intent to operate the vehicle10(Vehicle Start), e.g., through a key-on action including transitioning the vehicle ignition switch from off to on (OFF ->ON), the isolation switch device164remains in the open state (OPEN). The low-voltage battery235supplies required electric current to the accessory power module225and the low-voltage electric power supply122of the control module120through the low-voltage power bus155via the isolation diode162, and the accessory power module225is activated to supply electric current to the low-voltage electric power supply122of the control module120as required. The vehicle10operates with the engine240in the engine-off state (OFF).

There can be a command to operate the engine240, which includes starting the engine240(Engine Start) and subsequently running the engine240(Engine Run). The command to operate the engine240may occur in response to an operator torque request or in response to an autostart control signal from the control module120, e.g., to provide power to increase state-of-charge of the high-voltage battery210during ongoing operation of the vehicle10. The command to operate the engine240preferably originates from the control module120.

Starting the engine240(Engine Start) includes activating the starter motor245(ON), causing it to draw electric current from low-voltage battery235via the low-voltage power bus155. The isolation switch device164remains in the open state (OPEN) during the period of time when the starter motor245is activated (ON). The presence of the isolation diode162and the isolation switch device164in the open state (OPEN) causes all electric current flow to the starter motor245to be drawn from the low-voltage battery235via the first bus segment155A. Coincidentally, the accessory power module225provides electric power to the low-voltage electric power supply122of the control module120and any other accessory power demands via the second bus segment155B. When the isolation switch device164is in the open state (OPEN), the first bus segment155A is electrically separated from the second bus segment155B, i.e., there are two electrically separated low-voltage DC electric power buses for transferring low-voltage DC electric power within the vehicle10. Thus, the low-voltage electric power supply122of the control module120and any other accessory power devices connected to the second bus segment155B are electrically isolated from transient power voltages resulting from electric current flow to the starter motor245associated with starting the engine240.

When the engine240is running (ON) and the starter motor245is no longer activated (OFF), the isolation switch device164is controlled to the closed state (CLOSED), allowing electric current to flow in either direction between the first bus segment155A and the second bus segment155B, bypassing the isolation diode162.