Power Control System: Description and Operation
IMA SystemThe IMA (integrated Motor Assisted) system is a highly-efficient parallel hybrid drive system consisting of a main power unit (gasoline-fueled engine) and the assist unit (electric IMA motor).
The engine is 60°, V6 power plant that has a displacement of 2,997 liters. To reduce fuel consumption, the IMA system is equipped with i-VTEC, lean-burn control and valve pause system that reduces engine pumping loss and increases the regeneration of electric energy during deceleration.
The IMA motor, directly connected to the engine crankshaft, functions as a generator during deceleration, an engine starter, and a motor to assist the engine that drives the wheels.
The IMA system contains the DC 144 V battery and AC synchronous motor, control system, and related accessories. For optimal electrical safety, the intelligent power unit (IPU) is located behind the rear seat.
IMA Torque On-demand Control
Depending on the output torque requirements from the driver, A/T, cruise control, TCS, and ABS, the powertrain control module (PCM) controls the total output of the engine and the IMA motor by controlling the variable cylinder management (VCM), the electric throttle control system (ETCS), and the IMA system. With this IMA torque on-demand control, the driving performance and the fuel efficiency are improved. The PCM controls the output of the engine and the IMA motor in the following five methods with the required torque and the engine speed. Depending on the condition of the engine, IMA system, A/T, HVAC, and other systems, the control methods are modified.
Area 1
When maximum output torque is required, the engine is driven by six cylinders with wide open throttle, and the IMA motor assists the engine to increase torque.
Area 2
At high engine speed except wide open throttle and deceleration, the engine is driven by six cylinders without assist from the IMA motor.
Area 3
When partial output torque is required at low engine speed, the engine is driven by three cylinders and the IMA motor assists the engine to increase output torque. This control method saves fuel consumption during acceleration.
Area 4
When low output torque is required at low engine speed, the engine is driven by three cylinders without assist from the IMA motor. This control method saves fuel consumption during cruise and light load conditions.
Area 5
During deceleration, the PCM stops the fuel injection to all cylinders, and the IMA motor functions as a generator to charge the IMA battery. The intake and exhaust valves of the rear bank are deactivated by the VCM to reduce mechanical friction and increase the energy for charging.
Engine start
The IMA system drives the IMA motor, starts the engine at normal start, and restarts the engine after auto-stop. The IMA motor is directly connected to the engine crankshaft, so it is quieter than the 12 V starter. If a problem occurs with IMA system, for example, low battery module status of charge (SOC), low temperature, faulty IMA system, etc. The PCM receives a signal from the MCM and starts the engine with the 12 V starter.
Motor assisting function
During acceleration, energy is supplied from the battery module to the IMA motor, and the motor generates a maximum torque of 84.3 Nm (8.6 kgf-m, 62 ft. lbs.) to assist the engine. The PCM and MCM communicate to control the assist to maintain the battery module SOC within a specified range. When the battery module SOC is below the specified range, the MCM stops the assist to prevent over-discharge or damage to the battery. Assist is also not available when the IMA battery is very cold or very hot.
Regenerative control (at deceleration)
During deceleration, the IMA motor, driven by the wheels, functions as a generator. It charges the battery module by generating electrical energy. This is done by converting the kinetic energy of the vehicle during braking into electric energy that is stored in the IMA battery. When the battery module is full, regeneration stops to prevent overcharge of the battery.
Auto Idle Stop System
The auto idle stop system stops the engine automatically when the vehicle comes to a stop to reduce fuel consumption and minimize tailpipe emissions. When the following operating conditions are met, the auto idle stop will occur.
When the following engine restart conditions are met, the ECM restarts the engine by driving the IMA motor via the MCM and restarting fuel injection.
Auto Stop Indicator
When auto idle stop is operating, the auto stop indicator blinks. If the driver's door is opened during auto idle stop, the auto stop indicator blinks and the warning buzzer sounds to remind the driver that auto stop is in operation.
Motor Control Module (MCM)
The MCM controls the IMA motor, via the motor power inverter (MPI) module, to control the assist and regeneration. The MCM computes the battery module state of charge (SOC) and controls the IPU module fan.
Motor Power Inverter (MPI) Module
The MPI converts 144 V DC power into 3-phase AC power to run the electric motor during assist. During regeneration, the MPI converts AC voltage to DC. The system's SOC is computed by the MCM using voltage, temperature, input current, and output current readings from the battery module.
The MPI module controls the DC/AC conversion (from the IMA battery's 144 V DC to the IMA motor's 3-phase AC and vice versa).
The MPI module is air cooled. The heat fed through the heat sink is exhausted to the trunk compartment and outside the vehicle by the IPU module fan.
IMA Motor
The IMA motor is a synchronous AC type that converts electrical energy into kinetic energy, assists the engine during acceleration, and starts the engine.
The motor is located between the engine and the transmission. It consists of a 3-phase coil stator and a permanent magnet rotor that is directly connected to the engine crankshaft. A motor rotor position sensor is mounted on the back of the engine block to detect the position of the rotor.
Battery Module
A light-weight and compact Ni-MH (nickel-metal hydride) battery supplies energy to the IMA system.
The battery has 10 modules that are connected in series. Within each module are 12, 1.2 V cells. Total battery voltage is a nominal 144 V, and maximum capacity is 6.0 Ah.
The battery module has three built-in thermistor-type temperature sensors, and a PTC (positive temperature coefficient)-type temperature sensor for each cell.
Battery Module Switch
The battery module switch is connected in series to the battery module fuse. Always turn the battery module switch to the OFF position whenever service or checks are required on or around the high voltage circuits. Follow the service precautions.
Junction board
The junction board, located next to the battery module, distributes high voltage energy to the IMA system. The contactors, "Y" capacitor, bypass resistor, A/C compressor driver fuse, and the battery current sensor are all on the junction board.
Contactors
The high voltage contactor and bypass contactor are connected at the positive (+) output side of the battery module. These contactors are controlled by the MCM, connecting the IMA battery to the high voltage circuits. The current flows through the bypass contactor and bypass resistor first.
DC-DC Converter
Instead of using an alternator to maintain the 12 V battery, the electrical system uses a DC-DC converter. The converter converts high voltage direct current into low voltage direct current with little energy loss.
The DC-DC converter will illuminate the charging system indicator in the gauge assembly if a problem is detected in the 12 V charging system.
The DC-DC converter has a temperature monitoring system that will signal the MCM if its temperature is abnormally high. If needed, the MCM can signal the DC-DC converter to shut down.
Heat generated by the DC-DC converter is exhausted to the trunk compartment by the IPU module fan.
The DC-DC converter can also generate PGM-FI and/or IMA DTCs.
IPU Module Fan
The battery module, MPI module, and DC-DC converter generate heat during assist/regeneration. The IPU is equipped with a fan to cool it down, assure proper battery performance, and protect the system. The fan has a control circuit and rotation sensor that are controlled by the MCM. The cooling air is drawn into the battery module from the top of the rear tray, then it is exhausted into the trunk compartment and outside the vehicle through the MPI module heat sink, the DC-DC converter, and the A/C compressor driver heat sink.
