Hybrid Engine Controls - Description and Operation Cadillac Escalade GMT900

Overview

The drive motor generator power inverter module (PIM) assembly converts high voltage direct current (DC) electrical energy to 3 phase alternating current (AC) electrical energy. The accessory DC power control module (APM) converts high voltage DC electric energy into low voltage (14V) and intermediate voltage (42V) in order to charge the vehicles accessory battery and supply electric energy to the 42V power steering system. The APM and PIM are fastened together and are referred to as the drive motor generator control module assembly. The drive motor generator control module assembly is cooled with pre-mixed Dexcool® circulating through a cooling system that is separate from the engine cooling system. The hybrid cooling system utilizes a heat exchanger at the front of the vehicle and electric pumps to circulate the coolant. The engine control module (ECM) monitors a temperature sensor in the hybrid cooling system and operates the radiator fan and the hybrid coolant pumps in response to system temperature.

Direct Current (DC)

The drive motor generator control module assembly is connected to each pole of the high voltage (HV), direct current (DC) drive motor generator battery. Both of the negative and positive HV DC battery poles are isolated from the vehicle chassis by a specific amount of resistance. Each HV DC cable is switched ON or OFF by a high voltage, high current contactor relay contained within the drive motor generator battery assembly. All HV DC negative and positive DC cables are individually shielded and orange in color to alert the technician to the potential presence of high voltage. The electric air conditioning compressor high voltage DC cables are externally connected at the drive motor generator control module assembly. The APM and PIM share an internal connection that supplies the APM with high voltage DC current.

Three Phase Alternating Current (AC)

Three cables connect each motor generator to the PIM. Each individually shielded cable is orange in color to alert the technician to the potential presence of high voltage.

Intermediate and Low Voltage Circuits

The APM converts high voltage 300V DC current into both intermediate voltage, 42V, and low voltage, 12V, current.

Intermediate Voltage 42V Direct Current

Intermediate voltage 42V cables are individually shielded and are blue in color to alert the technician to the potential presence of intermediate voltage.

Low Voltage (12V) Direct Current

Low voltage (12V) cables on the hybrid-electric vehicle do not require unique coloring or servicing procedures.

Contained within the PIM assembly are the hybrid powertrain control module (HPCM), and two motor control modules (MCM). Each MCM controls its respective motor generator. All three modules are flash-programmable micro-processors.

Location

The HPCM is a non-serviceable, flash-programmable micro-processor contained within the PIM assembly.

Operating Functions

The HPCM is the main controller of hybrid operation. The HPCM determines when to perform hybrid operation modes such as engine Auto-stop and regenerative braking. The HPCM also operates in conjunction with the battery energy control module (BECM) to determine when to enable and disable the DC high voltage circuits. Each MCM operates the applicable electric motor generator based upon HPCM commands.

Communication and Hosted Diagnostics

The HPCM is the host controller for diagnostic trouble code (DTC) information for the following control modules

1. Accessory DC power control module (APM)
2. Battery energy control module (BECM)
3. Motor control module (MCM) 1
4. Motor control module (MCM) 2
5. Auxiliary transmission fluid pump (ATFP) control module

These modules diagnose their own operation and determine when a fault condition is present. Diagnostic status is communicated to the HPCM through the following circuits

1. APM utilizes the GM Hi-speed, Hybrid LAN communication circuit
2. BECM utilizes the GM Hi-speed, Hybrid LAN communication circuit
3. Each MCM and the HPCM exchange information and commands on the SPI bus internal communication circuit as well as the hi-speed hybrid GMLAN communication circuit.
4. ATFP control module utilizes a dedicated diagnostic status circuit

In the event a hosted module communicates a fault condition, the HPCM will determine if hybrid operation is effected and notify the vehicle operator by requesting the MIL illuminate and/or by displaying a hybrid service required message. In addition, the HPCM will store the associated DTC information for retrieval by a scan tool. Some hosted modules may require an ignition cycle to clear certain DTCs from the HPCM.

Circuit Inputs

In addition to GMLAN parameters, the HPCM directly monitors the following signal circuits

1. Transmission shift selector internal mode switch (IMS) Direction and Park/Neutral switch signals
2. Engine crankshaft position (CKP) sensor signal
3. ATFP diagnostic circuit
4. High voltage interlock circuit (HVIC)

Circuit Outputs

In addition to GMLAN and SPI bus commands, the HPCM directly controls the following output circuits

1. ATFP control circuit
2. BECM high voltage contactor relay pulse width modulated (PWM) control circuit

Each electric motor generator located within the transmission assembly is controlled by its own motor control module (MCM) flash-programmable, micro-processor. Each MCM is contained within the PIM. Also contained within the PIM is the hybrid powertrain control module (HPCM) micro-processor.

Each MCM operates the applicable electric motor generator based upon HPCM commands. Each MCM controls the speed, direction and output torque of its respective traction motor through the sequencing actuation of high current switching transistors called insulated gate bipolar transistors (IGBTs).

In addition to the internal SPI bus communication circuit between the HPCM and each MCM, the MCMs also communicate on the Hi-speed and Hybrid GMLAN communication circuits. The MCM does not store its own diagnostic trouble code (DTC) information. The HPCM will store MCM associated DTC information for retrieval by a scan tool. The scan tool can communicate directly with each MCM in order to retrieve data parameters only.

In addition to GMLAN parameters, each MCM monitors its respective motor generator for voltage, current, speed, direction and temperature. Additionally, the MCM monitors the IGBT components for temperature and proper operation. Some of the MCM operation data is shared with the HPCM.

Each MCM controls its respective IGBT driver board that in-turn controls each motor generator. The motor generators operate using three-phase alternating current (AC) electricity. Three cables connect each motor generator to the PIM. Each individually shielded cable is orange in color to alert the technician that the potential for high voltage is present.

The APM is affixed to and located underneath the PIM. It is fastened to the PIM with external mounting fasteners and 2 internal high voltage circuit connection fasteners. The APM shares a coolant passage with the PIM and as such is gasketed to the PIM.

The APM is the device which converts high voltage (300V) direct current (DC) to low voltage (12V) DC for accessory electrical operation and to charge the 12 volt accessory battery. The APM also converts HV DC to intermediate (42V) DC to supply the electric power steering system with voltage. The APM is capable of supplying up to 175 Amps of 12 volt DC and up to 50 Amps of 42 volt DC. In Jump Assist mode the APM converts 12 volt DC to HV DC to charge the high voltage hybrid batteries. The APM is capable of supplying up to 2.7 Amps at 290 volts DC on the high voltage circuit when operating in Jump Assist. An external 12V DC battery charger is required during the Jump Assist mode because the APM and vehicle controllers may draw as much as 80 Amps of current from the vehicles 12 volt DC system.

The APM has internal diagnostic tests that run at both power-up and during operation. All DTCs from the APM are reported to and hosted by the HPCM. The APM communicates directly only with the HPCM and only on the high speed hybrid GMLAN communication circuit.

Inputs supported by the APM include the high voltage and 12 volt circuits. The APM also monitors various internal components for current, voltage and temperature. The APM is also connected to the high speed hybrid GMLAN communication circuit. An individual 12 volt discrete circuit powers ON the APM. The APM will not begin conversion of voltage however, until the appropriate GMLAN enable signal is communicated to it by the HPCM.

The only outputs supported by the APM are the 12 volt and 42 volt conversion during normal vehicle operation and high voltage conversion during Jump Assist.

Vehicles are typically subject to certain legal requirements that limit the amount of electromagnetic interference (EMI) that can be generated by the vehicles electronic devices. Additionally, the electronic devices within the vehicle must be able to withstand a certain amount of EMI without effecting their operation. EMI is generated whenever electrical current flows through a circuit. The amount of EMI generated, or amplitude, is usually dependant upon the amount of current flow, amperage, and the on-off pattern of current flow through the circuit, frequency. The EMI requirements are generally referred to as electromagnetic compatibility (EMC).

There are many ways of ensuring the vehicle meets EMC requirements. These include

1. Adding capacitors and resistors to certain electrical circuits
2. Regulating the frequency at which a component may operate
3. Shielding the wires, cables and components

Circuit Design

The drive motor generator power inverter module (PIM) and the accessory DC power control module assembly (APM) each contain filter capacitors connected to the high voltage circuits. These capacitors are necessary to reduce the voltage spikes that occur as a result of the switching of current On and Off. Reducing voltage spikes reduces EMI. The frequency of current switching is also closely regulated. Too high a frequency can cause an increase in EMI generation.

Wiring/Cable Design

Different types of wire/cable shielding methods are utilized in the vehicle. Common types of circuit shielding include twisted-pair and internal braid or foil. Twisted pair is typically used in circuits such as high speed GMLAN communication circuits. The wire pair is twisted together at a particular turns-per-length ratio. Shielded cable is utilized for all other circuits requiring either protection from external EMI or to reduce EMI radiation of the cable itself into other nearby components or circuits.

High Voltage Cable

1. Battery Positive and Negative 300V Cable Assembly
2. Drive Motor Generator Power Inverter Module 3 Phase Cable Assembly
3. Air Conditioning Compressor Assembly

The high voltage cables utilize internal braid shielding. Typically, both ends of the internal braid shield are attached to chassis ground. All of the high voltage, internally shielded cables are grounded at their cable end attachment points. Mounting blocks, where used, perform the shield to chassis ground connection. Connection points not serviced with a mounting block utilize a separate ring terminal.

Low and Intermediate Voltage Wiring

The signal circuits for the transmission sensors utilize shielding protection. The drive motor generator position sensor and temperature sensor circuits utilize internal foil shielding. The wiring harness external of the transmission assembly is connected to chassis ground with ring terminals at the drive motor control module assembly. The internal transmission wiring harness is attached to chassis ground with a ring terminal at the valve body assembly.

The auxiliary transmission fluid pump (ATFP) 3 phase cables utilize internal foil shielding. The wiring harness shield is connected to chassis ground within the ATFP control module.

The power steering intermediate voltage wiring utilizes internal foil shielding. The wiring harness shield is connected to chassis ground at the APM connector and within the power steering motor assembly.

Component Shielding

Certain components utilize their structure to effectively shield EMI. Metal covers, chassis grounded metal cases and electro-magnetically conductive gaskets may all be part of a components EMC design.

Shielding Loss

A loss of proper shielding may result in poor AM band radio reception and/or incorrect sensor circuit readings depending upon the location of the shield loss. High voltage cables are not repairable. No attempt should ever be made to repair any portion of high voltage cables. Certain Low and Intermediate voltage shielded wiring harnesses may be repairable. Refer to Wiring Repairs .

High Voltage Monitoring Systems Description

The hybrid system monitors several high voltage components for attempted access. Additionally, a minimum amount of isolation resistance is maintained at all times between both negative and positive poles of the hybrid battery and the vehicle chassis. The drive motor generator power inverter module (PIM) microprocessors and the battery energy control module (BECM) monitor the hybrid system for access and loss of isolation detection.

High Voltage Interlock Circuit (HVIC)

The HVIC is a wire loop that passes through certain high voltage components. The HVIC is used to determine if access to high voltage components is being attempted. The opening of these high voltage components causes the HVIC to open. The hybrid system may react to the loss of HVIC continuity by opening the high voltage contactor relays and discharging the high voltage capacitors. The HVIC signal is generated by the BECM. The HVIC status is monitored by each motor control module (MCM) as well as the hybrid powertrain control module (HPCM) and the BECM.

High Voltage dc Chassis Isolation

The hybrid system monitors the electrical potential between high voltage and the vehicle chassis. High voltage should always be isolated from the vehicle chassis by a certain amount of resistance to avoid the potential for a life threatening current path. In the event that a high voltage leak path is detected to the vehicle chassis, the hybrid system will set a diagnostic trouble code (DTC). High voltage DC chassis isolation is monitored by both the MCMs and the BECM.

Testing for isolation requires special tools and procedures. Because of the high voltages present in the hybrid system, a loss of isolation may occur due to insulation breakdown. Insulation breakdown typically occurs only when high voltages and/or current is present. Conditions such as insulation breakdown cannot be diagnosed with a typical DMM because high voltage is not used by the DMM when measuring resistance.

Hybrid Modes of Operation Description

This overview is not a comprehensive list of all aspects of the Two-Mode Hybrid vehicle. Refer to Electronic Component Description for information regarding transmission operation. More detailed and comprehensive information is also available through the dealer training program.

Engine Starting

This vehicle does not use a 12 V starter motor to crank the internal combustion engine (ICE). A much more powerful 300 V motor/generator located within the transmission is utilized to crank the engine. The 300 V drive motor generator can rotate the engine to operating speed (800 RPM) within just a few hundred milliseconds. The 300 V drive motor generator allows near-instant starting of the engine. Once started, engine operation may cycle between Autostop (engine off) and Autostart (engine running) for the duration of the drive trip.

Autostop

After a successful engine start, the hybrid powertrain control module (HPCM) may turn off the engine and operate in the Autostop mode. Some of the vehicle conditions that allow the engine to stop running and enter the Autostop mode include

1. Vehicle power mode is correct: The ignition switch is in the Run position after first being turned to the crank position which resulted in a successful engine start, OR The ignition switch is turned to the Run position after a successful remote vehicle start request.
2. Hood switch position status is Closed.
3. ECM is not requesting continued engine operation for diagnostic purposes.
4. Gear selector is not in the Reverse or Manual position.
5. Hybrid battery state of charge (SOC) is more than 20 percent.
6. Hybrid battery voltage, temperature or power limits are not exceeded.
7. Engine coolant temperature (ECT) is more than an acceptable limit.
8. Drive motor generator temperature limits are not exceeded.
9. Drive motor generator power inverter module (PIM) temperature limits are not exceeded.
10. No hybrid system faults exist.

A chime will sound if the drivers door is opened while in Autostop as a reminder that the engine is not in the OFF mode.

Engine OFF and AUTOSTOP modes are indicated on the tachometer display.

1. When the tachometer needle indicates OFF, the engine is not running and will remain Off until the ignition key is placed in the Crank position or a remote vehicle start request is received from the keyless entry transmitter.
2. When the tachometer needle indicates AUTOSTOP, the engine is not running but may Autostart at any time without notice.

Autostart

The Two-Mode Hybrid vehicle does not require internal combustion engine (ICE) operation at all times. After a successful engine start, the hybrid powertrain control module (HPCM) may turn off the engine (Autostop) when not required for the current vehicle conditions. The engine will remain off while in Autostop mode, until such time that vehicle conditions require the engine to run. The near-instant starting of the engine from Autostop mode is called Autostart. Some of the vehicle conditions that may cause the HPCM to exit the Autostop mode and Autostart the engine include

1. Hood switch position status changes to Open
2. ECM Request
3. Gear selector is placed in the Reverse or Manual position
4. Hybrid battery SOC is too low
5. Hybrid battery voltage, temperature or power limits are exceeded
6. Engine coolant temperature (ECT) is too low
7. Drive motor generator temperature limits are exceeded
8. Drive motor generator power inverter module (PIM) temperature limits are exceeded
9. A hybrid system fault is observed
10. Electric Launch capability has been exceeded and engine operation is required

Electric Launch/Assist - EV Mode

The transmission assembly contains two 300 V drive motor generator assemblies. These powerful 60 kW drive motor generators are capable of propelling the vehicle while the engine is in the Autostop mode or they may assist an already running engine. Depending upon accelerator pedal position, the vehicle may be propelled solely with the electric drive motor generators at speeds exceeding 41 km/H (26 mph) before assistance from the engine is required. The engine will Autostart when driving conditions require engine assistance. During engine running conditions, the torque provided by the drive motor generators is supplemented with the engine torque output.

Regenerative Braking

When the vehicle is coasting or braking the HPCM may operate the drive motor generators in an electrical generation mode. Operating as electrical generators, the drive motor generators exert a driveline load that helps to slow the vehicle. The electrical energy that the drive motor generators create is transferred by the drive motor generator power inverter module (PIM) to the drive motor generator battery assembly (hybrid batteries). Constant communication between the HPCM and the electronic brake control module (EBCM) allows the blending of regenerative braking force with hydraulic braking force.

Enhancements to Engine Operation

While not unique to the Two-Mode hybrid vehicle, the following modes of operation benefit from expanded operational ranges. Expanded operational range is possible because the drive motor generators can be utilized to smooth driveline disturbances that would be objectionable without the intervention of the drive motor generator.

Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The ECM monitors the corresponding changes in the TP, the MAP, and the MAF. The ECM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to prevent damage to the catalytic converters. This mode is activated more quickly and for a longer duration in the Two-Mode hybrid vehicle.

Cylinder Deactivation (Active Fuel Management)

To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the cylinder deactivation system ON to deactivate engine cylinders 1 and 7 on the left bank, and cylinders 4 and 6 on the right bank, switching to a V4 mode. The engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications. This mode is activated more quickly and for a longer duration in the Two-Mode hybrid vehicle.

See also:
• Wiring Repairs
• Electronic Component Description