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 an inline 4-cylinder, 8-valve power plant that has a displacement of 1,339 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 158 V battery and AC synchronous motor, control system, and related accessories. For safety, the intelligent power unit (IPU) is located behind the rear seat.
Operating Condition
Vehicle stop mode (idle stop)
The engine stops idling if the IMA battery has enough electricity left.
Start running mode (Engine and IMA motor)
The engine runs with low lift cam. The IMA motor assists torque.
Slow acceleration mode (Engine only)
The engine runs with low lift cam. The IMA motor does not assist.
Low speed cruise mode (IMA motor only)
The IMA motor runs the vehicle by itself if the IMA battery has enough electricity left. The intake and exhaust valves pause to reduce valve spring compression and pumping loss.
Acceleration from low speed mode (Engine and IMA motor)
The engine runs with low lift cam. The IMA motor assists torque.
High acceleration from low speed mode (Engine and IMA motor)
The engine runs with low lift cam. The IMA motor assist torque.
High speed cruise mode (Engine only)
The engine runs with low lift cam. The IMA motor does not assist.
Deceleration mode (IMA battery charge)
The intake and exhaust valves pause to reduce engine braking force. The IMA motor prevents engine braking force by charging the IMA battery.
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 103 Nm (10.5 kgf-m, 76 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 overall fuel consumption and minimize tailpipe emissions. When the following operating conditions are met, auto idle stop will occur.
When the following engine restart conditions are met, the PCM restarts the engine by driving the IMA motor via the MCM and restarting fuel injection.
Engine restart conditions
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.
Battery Condition Monitor (BCM) Module
The BCM module computes the battery module state of charge (SOC) and controls the IPU module fan. The system's SOC computed by the BCM module using voltage, temperature, input current, and output current readings from the battery module.
Motor Control Module (MCM)
The MCM converts 158 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 MCM module controls the DC/AC conversion (from the IMA battery's 158 V DC to the IMA motor's 3-phase AC and vice versa).
The MCM module is air cooled. The heat fed through the heat sink is exhausted to the trunk compartment and outside of vehicle by the IPU module fan.
The MCM controls the IMA motor to control the assist and regeneration.
IMA Motor
The IMA motor is a synchronous AC type that converts electrical energy into kinetic energy and vice versa. It 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 11 modules that are connected in series. Within each module are 12 1.2 V cells. Total battery voltage is a nominal 158 V, and maximum capacity is 5.5 Ah.
The battery module has 3 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, mounted on the battery module, distributes high voltage energy to the IMA system. The contactors, bypass resistor, and the battery current sensor are all on the junction board.
Contactors
The high voltage contactor and bypass contactor are connected at the negative (-) output side of battery module. These contactors are controlled by the BCM module, connecting the IMA battery to the high voltage circuits. The current flows through the bypass contactor and bypass resistor at start-up.
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 BCM module if its temperature is abnormally high. If needed, the BCM module 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, the MCM, the A/C compressor driver, and the 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 BCM module. 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 of vehicle through the MCM heat sink, the DC-DC converter, and A/C compressor driver heat sink.
Power Cables
The IMA motor power cable connects the IMA motor and the motor control module (MCM). The cable feeds through an aluminum tube for damage protection and to prevent noise. The A/C compressor power cable also goes through the aluminum tube. Another aluminum tube, parallel to the IMA motor/A/C compressor tube, houses the DC/DC converter cable. These pipes are connected in one piece with the pipe clamp (orange), and attached under the vehicle.
