Part 1
CONTROL SYSTEMELECTRONIC ENGINE CONTROL (EEC) SYSTEM
The EEC system provides optimum control of the engine through the enhanced capability of the powertrain control module (PCM). The EEC system also has an on board diagnostic (OBD) monitoring system with features and functions to meet federal regulations on exhaust emissions.
The electronic engine controls consist of the following:
- Powertrain control module (PCM)
- Cylinder head temperature (CHT) sensor
- Camshaft position (CMP) sensor
- Crankshaft position (CKP) sensor
- Mass air flow (MAF) sensor
- Heated oxygen sensor (HO2S)
- Catalyst monitor sensor (CMS)
- Knock sensor (KS)
The EEC system has 2 major divisions: hardware and software. The hardware includes the PCM, sensors, switches, actuators, solenoids, and interconnecting terminals. The software in the PCM provides the strategy control for outputs (engine hardware) based on the values of the inputs to the PCM. EEC hardware and software are described in this section.
The PCM receives information from a variety of sensor and switch inputs. Based on the strategy and calibration stored within PCM, the PCM generates the appropriate output. The system is designed to minimize emissions and optimize fuel economy and driveability. The software strategy controls the basic operation the engine, provides the OBD strategy, controls the malfunction indicator lamp (MIL), communicates to the scan tool over the data link connector (DLC), allows for flash electrically erasable programmable read only memory (EEPROM), provides idle air and fuel trim, and controls failure mode effects management FMEM).
POWERTRAIN CONTROL MODULE
The center of the electronic engine control (EEC) system is a microprocessor called the PCM. The PCM receives input from sensors and other electronic components. Based on information received and programmed into its memory, the PCM generates output signals to control various relays, solenoids, and actuators. The hybrid vehicle uses a 150-pin PCM which has 3 separate electrical harness connectors.
The PCM is located behind the instrument panel (cowl), center to both driver and passenger sides (access from the engine compartment).
PCM Power And Grounds:
CYLINDER HEAD TEMPERATURE (CHT) SENSOR
The CHT sensor is a thermistor device in which the resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
The CHT sensor is installed in the aluminum cylinder head and measures the metal temperature. The CHT sensor can provide complete engine temperature information and can be used to infer coolant temperature. If the CHT sensor conveys an overheating condition to the PCM, the PCM then initiates a fail-safe cooling strategy based on information from the CHT sensor. A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Using both the CHT sensor and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp home capability.
CAMSHAFT POSITION (CMP) SENSOR
The CMP sensor is a variable reluctance sensor that detects the position of the camshaft. The CMP sensor identifies when piston number 1 is on its compression stroke. A signal is then sent to the PCM and used for synchronizing the firing of sequential fuel injectors. The PCM also uses the CMP signal to select the proper ignition coil to fire. The input circuit to the PCM is referred to as the CMP input or circuit.
CRANKSHAFT POSITION (CKP) SENSOR
The CKP sensor is a magnetic transducer mounted on the engine block adjacent to a pulse wheel located on the crankshaft. By monitoring the crankshaft mounted pulse wheel, the CKP is the primary sensor for ignition information to the PCM. The pulse wheel has a total of 35 teeth spaced 10 degrees apart with one empty space for a missing tooth. By monitoring the pulse wheel, the CKP sensor signal indicates the crankshaft position and speed information to the PCM. By monitoring the missing tooth, the CKP sensor is also able to identify piston travel in order to synchronize the ignition system and provide a way of tracking the angular position of the crankshaft relative to a fixed reference. The PCM also uses the CKP signal to determine if a misfire has occurred by measuring rapid decelerations between pulse wheel teeth.
MASS AIR FLOW (MAF) SENSOR
The MAF sensor uses a hot wire sensing element to measure the amount of air entering the engine. Air passing over the hot wire causes it to cool. This hot wire is maintained at 200° C (392° F) above the ambient temperature as measured by a constant cold wire. If the hot wire electronic sensing element must be replaced, then the entire assembly must be replaced. Replacing only the element may change the air flow calibration.
The current required to maintain the temperature of the hot wire is proportional to the volume of air flow. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio.
The MAF sensor is located between the air cleaner and the throttle body inside the air cleaner assembly.
HEATED OXYGEN SENSOR (HO2S)
The HO2S detects the presence of oxygen in the exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a voltage signal greater than 0.6 volt. The HO2S provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation. The HO2S generates a voltage between 0.0 and 1.1 volts.
Embedded with the sensing element is the HO2S heater. The heating element heats the sensor to temperatures of 800° C (1,400° F). At approximately 300° C (600° F) the engine can enter closed loop operation. The VPWR circuit supplies voltage to the heater and the PCM turns on the heater by providing the ground when the proper conditions occur. The heater allows the engine to enter closed loop operation sooner. The use of this heater requires that the HO2S heater control be duty cycled to prevent damage to the heater.
KNOCK SENSOR (KS)
The KS is a tuned accelerometer on the engine which converts engine vibration to an electrical signal. The PCM uses this signal to determine the presence of engine knock and to retard spark timing.
HYBRID ELECTRIC SYSTEM
The hybrid electric system consists of 3 key components: the internal combustion engine, the electronically controlled continuously variable transaxle (CVT), and the high voltage traction battery. In this powertrain configuration, there are 2 power sources that are connected to the driveline: a combination of the engine and the generator which uses a planetary gear set to connect to each other, and the electric traction motor which is connected to the drive wheels.
The high voltage traction battery is an electric energy storage device. The electric energy is used by the generator motor and the traction motor.
The planetary gear set functions as an electronically controlled CVT between the carrier gear (engine) and the ring gear (traction motor) which is connected to the drive wheels. This is achieved by controlling the sun gear (generator) speed and direction. The reason this is an electronically controlled CVT is due to the property of the planetary gear set in which the torque relationships between the sun gear, the carrier gear, and ring gear are fixed for this mechanical design. Therefore, the planetary gear set can also be viewed as a device that splits the engine output power to the driveline and to the generator motor.
There are 2 paths for the engine to deliver its output power: from the engine to the carrier gear, to the ring gear, to the intermediate shaft (mechanical path), and from the engine to the carrier, to the sun gear, to the ring gear and to the intermediate shaft (electrical path). The combination of the mechanical and the electrical paths makes this powertrain similar to a conventional vehicle powertrain with a CVT.
The electric traction motor uses power supplied by the high voltage traction battery and provides propulsion to the vehicle independently from the engine. Both power sources, a combination of the engine and the generator and the electric traction motor, can propel the vehicle simultaneously and independently.
This powertrain configuration is able to achieve better than conventional powertrain fuel economy and lower emissions levels because:
- the engine operates in its most efficient operating regions whenever possible.
- the engine size can be reduced with the same vehicle performance because of the dual power sources.
- the engine operation can be better optimized since it can be stopped if operational conditions are not favorable to the fuel economy or emissions.
- the kinetic energy during braking can be captured and stored in the high voltage traction battery through regenerative braking.
The torque determination and energy management strategy controls and operates the powertrain system to satisfy driver demands, increase the fuel economy, and decrease emissions levels.
In order to achieve better fuel economy and lower emission levels, the powertrain control module (PCM) torque determination and energy management strategy operates the powertrain system with specified operational conditions. First, the torque determination and energy management strategy determines in real time how much torque the driver is requesting and how much torque each power source can deliver to the drivetrain. Then it chooses the most efficient power source for that operational condition. Some of the inputs to the energy management strategy include driver demand, traction battery state of charge, performance limitations of components, battery life (charging and discharging rate and cycling), driveability, ambient temperature, and barometric pressure.
The hybrid electric system is a torque based system. When the gear selector is placed in DRIVE, the driver is going to request a positive torque by pressing the accelerator pedal, or a negative torque by pressing the brake pedal. The positive torque is perceived as vehicle acceleration, and the negative torque as vehicle deceleration (braking).
The brake and the electric power assist steering systems remain fully functional when the engine is stopped by the PCM. This allows the driver to operate the vehicle in electric mode when the engine is off.
HYBRID ELECTRIC CONTROL SOFTWARE
There are 5 fundamental operating modes in the hybrid electric system:
- Electric mode
- Positive split mode
- Negative split mode
- Neutral gear mode
- Engine cranking mode
ELECTRIC MODE
The hybrid electric system operates in the electric mode when the vehicle is propelled by the electrical power stored in the high voltage traction battery. The torque is supplied to the output shafts by the traction motor, the generator motor, or a combination of both. This is a preferred mode whenever the desired torque is low and the electrical system, rather than the engine, can produce it more efficiently. The electric mode is also used in reverse because the engine can deliver torque only in a forward direction.
POSITIVE SPLIT MODE
In this mode the internal combustion engine is running and powering the generator motor which produces the electricity. The power from the engine is split between the path through the generator motor and the path to the output shafts of the vehicle. The electricity produced by the generator motor charges the high voltage traction battery or powers the traction motor. In this mode the traction motor can operate as a motor or as a generator to make up the difference between engine power and desired power at the wheels. This mode is preferred whenever the traction battery needs to be charged.
NEGATIVE SPLIT MODE
In this mode the internal combustion engine is running but the generator motor is reducing the engine speed. This mode is never preferred but occurs when all of the following vehicle conditions are met:
- The engine is running.
- The vehicle speed is high.
- The high voltage traction battery is charged.
- Reducing engine throttle is not desired.
NEUTRAL GEAR MODE
The hybrid electric system operates in this mode when the driver selects NEUTRAL. In neutral gear the electronically controlled CVT does not deliver any positive or negative torque to the output shafts of the vehicle. The neutral gear actually consists of 2 neutral operating states: active neutral activated above 10 km/h (6 mph), and passive neutral activated below 10 km/h (6 mph). In active neutral, the generator motor is permitted to start and stop the internal combustion engine as needed to maintain the high voltage traction battery charge, and provide A/C. In passive neutral, the engine must remain in the state it was (running or not running) when the mode was entered and is not permitted to change state (start or stop). If the engine is running when entering passive neutral, the speed control of the engine is transferred from the generator motor to the engine itself. The engine controlling its own speed in passive neutral is described as secondary idle. The vehicle cannot be started in passive neutral, but can be started in active neutral.
ENGINE CRANKING MODE
The electronically controlled CVT provides the engine cranking function to start or restart the internal combustion engine. When the PCM requests the engine cranking mode, the generator motor rapidly accelerates the engine speed up to about 1,000 RPM in about 0.3 seconds. When the engine speed reaches a calibrated speed the PCM commands the delivery of fuel and spark at the appropriate times.
