Integrated Motor Assist (IMA) System
IMA System
The Integrated Motor Assisted (IMA) system is a highly-efficient parallel hybrid drive system consisting of a main power unit (gasoline-fueled engine) and the subpower unit (electric IMA motor).
The engine is an inline 4-cylinder, 8-valve power plant that has a displacement of 1339 liters. To reduce fuel consumption, the IMA system is equipped with i-DSI, 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 IMA 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.
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, or faulty system, etc., the ECM 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 49 Nm (5 kgf-m, 36 ft. lbs.) to assist the engine. The ECM 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 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. The ECM stops the engine or keeps it running under the various operating conditions listed in the chart.
Auto Idle Stop System Operating Conditions
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.
Engine restart conditions
Auto Idle Stop Indicator
For CVT:
When auto idle stop is operating, the auto stop indicator blinks. If the driver's door is opened during auto idle stop, the auto idle stop indicator blinks and the warning buzzer sounds to remind the driver that auto idle stop is in operation.
For M/T:
When auto idle stop is operating, the auto stop indicator comes on.
When the indicator is on steady, the clutch pedal is being pressed.
When the indicator is blinking, the clutch pedal is not being pressed.
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.
The MCM converts 144 V DC power into 3-phase AC power to run the electric motor during assist. During regeneration, the MCM 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.
Motor Power Inverter (MPI) 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 into the heat sink is exhausted to the trunk compartment by the IPU module fan. The MPI module has a built-in temperature sensor. The sensor transmits temperature data to the MCM for protection.
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. Three commutation sensors are mounted inside the housing 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 20 modules that are connected in series. Within each module are six 1.2 V cells Total battery voltage is a nominal 144 V, and maximum capacity is 6.0 Ah.
The battery module has 3 built-in thermistor-type temperature sensors, and a PTC (positive temperature coefficient)-type temperature sensor for each cell.
Junction board
The junction board is mounted on the battery module. The battery module switch, contactors, fuses, and the battery current sensor are all on the junction board.
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.
Contactors
The high voltage contactor and bypass contactor are connected at the positive (+) output sic. 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 to charge the PDU capacitors.
DC-DC Converter
Instead of using an alternator to maintain the 12V 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 illuminates the conventional 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 signals 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.
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 fin 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 through the MPI module heat sink and the DC-DC converter heat sink.