System Description
HYBRID CONTROL SYSTEM
System Description
DESCRIPTION
General
The Hybrid Vehicle Control system optimally effects cooperative control of a QR25DE engine and a high speed, high-output MG2 through a hybrid transaxle that provides excellent transmission performance.
Furthermore, it uses a variable-voltage system consisting of a high-output HV battery with a nominal voltage of
DC 244.8 V, and a boost converter that boosts the operating voltage of the system to a maximum voltage of DC 650 V.
NOTE:
- Inverter water pump is also called water pump with motor and bracket assembly.
- Generator is also called MG1 or motor generator No.1.
- Traction motor is also called MG2 or motor generator No.2.
- Inverter assembly is also called inverter with converter assembly.
- Hybrid vehicle converter (DC/DC converter) is also just called DC/DC converter.
Driving Performance
This system uses a variable-voltage system that consists of a boost converter to boost the operating voltage to a maximum voltage of DC 650 V. It is able to drive the MG1 (Motor Generator No.1) and MG2 (Motor Generator No.2) at a high voltage, and minimizes the electrical loss associated with the supply of electric power at a smaller current. Thus, it is able to operate the MG1 and MG2 at high speeds and high outputs.
A high driving force is achieved through the synergy effect of the high-speed, high-output MG2 and the high efficiency QR25DE engine.
Fuel Economy Performance
- By optimizing the internal construction of MG2, this system realizes a high level of regenerative capability, thus realizing a high level of fuel economy performance.
- This system stops the engine while the vehicle is idling, and stops the engine as much as possible under conditions in which the operating efficiency of the engine is poor, allowing the vehicle to operate using only
MG2. Under the conditions in which the operating efficiency of the engine is favorable, the engine operates to drive the vehicle using MG1 while generating electricity. Thus, this system effects the input-output control of driving energy in a highly efficient manner to realize a high level of fuel economy.
FEATURES
General
- The Hybrid Vehicle Control System offers the following representative features:
- Uses a variable-voltage system in which a boost converter boosts the operating voltage of the system to a maximum voltage of DC 650 V and an inverter converts the direct current into an alternating current, which supplies the system voltage to MG1 and MG2.
- A motor speed reduction planetary gear unit, whose purpose is to reduce motor speed, is used to enable the high-speed, high-output MG2 to adapt optimally to the power split planetary gear unit in the hybrid transaxle.
- The Hybrid Vehicle Control System consists primarily of the following components:
Variable-Voltage System
In the Hybrid Vehicle Control System, a boost converter is used inside the inverter assembly. The boost converter boosts the system operating voltage to a maximum voltage of DC 650 V and the inverter converts direct current into alternating current, in order to drive MG1 and MG2 at a high voltage as well as minimize the electrical loss associated with the electric power supply at a smaller current. Thus, MG1 and MG2 can be operated at high speeds and high output.
Clutch-Less System
A clutch-less system is used to mechanically link the front wheels and MG2 via gears. To disengage the motive force in the neutral position, the shift position sensor outputs an N position signal to turn OFF all the power transistors in the inverter (which controls MG1 and MG2). As a result, the operation of MG1 and MG2 shuts down, thus rendering the motive force at the wheels to zero.
Hybrid Transaxle
- This system drives the vehicle by combining the motive forces of the engine and the MG2 in an optimal manner in accordance with the driving conditions of the vehicle. In this system, the engine power forms the basis. The power split planetary gear unit in the hybrid transaxle splits the engine power two ways: one to drive the wheels, and the other to drive MG1, so that it can function as a generator.
- This hybrid transaxle consists primarily of MG1, MG2, a compound gear unit (which consists of a motor speed reduction planetary gear unit and a power split planetary gear unit), a counter gear unit and a differential gear unit.
- The engine, MG1 and MG2 are mechanically joined via the compound gear unit.
- The compound gear unit contains a motor speed reduction planetary gear unit and a power split planetary gear unit. The motor speed reduction planetary gear unit reduces the rotational speed of MG2, and the power split planetary gear unit splits the motive force of the engine two ways: one to drive the wheels, and the other to drive MG1, so that it can function as a generator.
- In the motor speed reduction planetary gear unit, the sun gear is coupled to the output shaft of MG2, and the carrier is fixed. Furthermore, the compound gear unit uses a compound gear, in which two planetary ring gears, a counter drive gear and a parking gear are integrated.
Link-Less
The Electric Throttle Control Actuator is used. This is a link-less system that does not use an accelerator cable. Instead, it uses an accelerator pedal position sensor and a throttle position sensor to detect the accelerator pedal position and the throttle position.
The hybrid vehicle ECU calculates the target engine speed and the required engine motive force in accordance with the signals provided by the accelerator pedal position sensor, vehicle driving conditions, and the
SOC (state of charge) of the hybrid vehicle battery. The hybrid vehicle ECU sends the results of this calculation to the ECM via the CAN communication line. The ECM optimally controls the electric throttle control actuator and sends the actual engine speed signal to the hybrid vehicle ECU.
Regenerative Brake
The regenerative brake function operates MG2 as a generator while the vehicle is decelerating or braking and stores this electrical energy in the HV battery.
Basic Operation
This system generates a motive force in combination with the engine, MG1 and MG2 in accordance with the driving conditions. Representative examples of the various combinations are described below.
Starting (Drive by MG2)
Supply of electrical power from the HV battery to MG2 provides force to drive the front wheels.
During Acceleration with Engine
While the front wheels are being driven by the engine via the planetary gears, MG1 is driven by the engine via the planetary gears, in order to supply the generated electricity to MG2.
Charge The HV Battery
MG1 is rotated by the engine via the planetary gears, in order to charge the HV battery.
During Deceleration Driving
When the vehicle is decelerating, kinetic energy from the front wheels is recovered and converted into electrical energy and used to recharge the HV battery by means of MG2.
SYSTEM OPERATION
General
- The Hybrid Vehicle Control System uses two sources of motive force, the engine and MG2, and uses MG1 as a generator. The system optimally combines these forces in accordance with the various driving conditions.
- The hybrid vehicle ECU constantly monitors the SOC condition, the HV battery temperature, the coolant temperature, and the electrical load condition. If any one of the monitored items fails to satisfy the requirements when the READY indicator is ON and the shift lever is in the "P" position, or the vehicle is driven in reverse, the hybrid vehicle ECU to starts the engine to drive MG1, and then charges the HV battery.
- The Hybrid Vehicle Control System drives the vehicle by optimally combining the operations of the engine, MG1, and MG2 in accordance with the driving conditions listed below.
The vehicle conditions listed below are examples of typical vehicle driving conditions.
How to Read a Nomographic Chart
- The nomographic chart below gives a visual representation of the planetary gear's rotational direction, rotational speed, and torque balance.
- In the nomographic chart, a straight line is used to represent the relationship between the rotational speeds of the 3 gears in the power split planetary gear unit. The rotational speed of each gear is indicated by the distance from the 0 rpm point. Due to the structure of the power split planetary gear unit, the relationship between the rotational speeds of the 3 gears is always expressed by a straight line.
- The relationship between the gear rotation directions and the torque that acts on each gear is as described below.
Due to the structure of this hybrid transaxle, the MG2 motive force acts on the ring gear via the motor speed reduction planetary gear unit. The following illustrations of the power split planetary gear unit operation, represent the rotational direction, rotational speed and torque condition that act on the ring gear.
- The following nomographic charts and the illustrations of the power split planetary gear unit operation for each vehicle driving condition represent one situation as an example.
Normal Driving (During Low Load and Constant-speed Cruising)
(B): Starting with MG2
- When the vehicle is started off, the vehicle operates powered only by the MG2.
- When the vehicle starts off under normal conditions, it runs using the motive force of MG2. While driving under this condition, the rotational speed of the carrier is 0 rpm due to the engine being inactive. In addition, since MG1 does not generate any torque, no torque acts on the sun gear. However, the sun gear rotates freely in the (-) direction balancing the rotating ring gear (Output).
(C): Driving with MG2 and Starting Engine
- If the required drive torque increases when driving with MG2 only, MG1 is activated to start the engine.
In addition, if any one of the items monitored by the hybrid vehicle control ECU such as the SOC condition, the battery temperature, the engine coolant temperature or the electrical load condition deviates from the specified level, MG1 is activated to start the engine.
- Only when driving with MG2, when the engine starts with MG1, the torque acts on the sun gear (MG1) in the
(+) direction, the carrier (Engine) rotates in the (+) direction in reaction to the torque transmitted by the sun gear. The ring gear rotates in the (+) direction in reaction to the carrier rotation.
- The following nomographic charts and the illustrations of the power split planetary gear unit operation for each vehicle driving condition represent one situation as an example.
(D): During Low Load and Constant-Speed Cruising
- When the vehicle is driving under low load and constant-speed cruising conditions, the motive force of the engine is transmitted by the planetary gears. Some of this motive force is output directly, and the remaining motive force is used for generating electricity through MG1. Through the use of the electrical path of an inverter, this electrical power is transmitted to MG2 to be output as the motive force of MG2.
If the SOC level of the HV battery is low, it is charged by MG1 driven by the engine.
- The following represents an example of the power split planetary gear unit operation under normal driving conditions. The sun gear, carrier and ring gear rotate in the (+) direction. The torque from the engine acts on the carrier (Engine) in the (+) direction, causing the sun gear and ring gear to react in the (-) direction.
MG1 generates electricity by harnessing the (-) torque that acts on the sun gear.
- The following nomographic charts and the illustrations of the power split planetary gear unit operation for each vehicle driving condition represent one situation as an example.
(E): During Full Throttle Acceleration
- When the vehicle driving condition changes from low load cruising to full-throttle acceleration, the system supplements the motive force of MG2 with electrical power from the HV battery.
- When more engine power is required, in order to increase the engine speed, the rotation speeds of the related gears change as follows. The directions in which the torque acts on each gear are the same as those described in "During Low Load and Constant-speed Cruising".
(F): During Deceleration Driving
Deceleration in "D" Range
- While the vehicle is decelerated with the shift lever in the D position, the engine is turned OFF and the motive force changes to zero. At this time, the wheels drive MG2, causing MG2 to operate as a generator, charging the HV batteries.
- If the vehicle decelerates from a higher speed, the engine maintains a predetermined speed without stopping, in order to protect the planetary gear unit.
- During deceleration, the ring gear is rotated by the rear wheels. Under this condition, due to the engine being inactive, the rotational speed of the carrier is 0 rpm. In addition, since MG1 does not generate any torque, no torque acts on the sun gear. However, the sun gear (MG1) rotates freely in the (-) direction balancing the rotating ring gear (Output).
(G): During Reverse Driving
- When the vehicle is being driven in reverse, the required power is supplied by MG2. At this time, MG2 rotates in the opposite direction, the engine remains stopped, and MG1 rotates in the normal direction without generating any electricity.
- During reverse driving, when any of the SOC condition, battery temperature, engine coolant temperature and electrical load condition reaches a specified level, the engine may start. The following illustration represents the condition when the engine is not driving.
- The conditions of the planetary gear are opposite to those described in "Starting and Driving with MG2".
Due to the engine being inactive, the rotational speed of the carrier is 0 rpm but the sun gear (MG1) rotates freely in the (+) direction balancing the rotating ring gear (Output).
