At present, many domestic auto manufacturers are developing their own hybrid vehicles in the Honda i-MMD hybrid system. This article describes the key technologies of the Honda i-MMD hybrid system.
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Honda Accord i-MMD hybrid system structure
The configuration of the iMMD system is as follows:
The system consists of an Atkinson cycle engine, clutch, and dual motor, three-axis arrangement. The engine is connected to the engine output shaft through a clutch, and is connected to the generator through a gear before the clutch; the motor is directly connected to the motor output shaft; there is a third shaft between the engine output shaft and the motor output shaft, which transmits power to the wheel .
Drive mode
Pure electric mode, ie EV drive. In this mode, the engine does not work, the clutch is disconnected, and the motor directly outputs torque through the gear mechanism;
Hybrid mode in series, Hybrid drive. In this mode, the engine generates electricity through the generator, the clutch is disconnected, and the motor outputs torque through the gear mechanism;
Parallel hybrid mode, ie Engine drive. In this mode, the engine directly outputs torque, the clutch is combined, and the motor simultaneously outputs torque.
The above three modes are the Multi-Modes of the Accord Multi-Modes Drive system. So where is the intelligent represented by i? i is reflected in Honda's optimization of the control strategy.
iMMD system control strategy optimization
The iMMD system further enhances economics in two ways between three operating modes:
(1) Improve fuel economy as much as possible in each mode;
(2) Switch modes to improve fuel economy.
1. Improve fuel economy as much as possible in each mode
In the Hybrid/Engine drive mode, based on the original operating conditions, the controller further improves the engine efficiency by changing the engine/motor operating point, as shown in the figure:
The illustration is the MAP map of the engine. The abscissa is the rotational speed and the ordinate is the torque. The color is warm and cold, indicating the output efficiency of the engine. The blue and yellow dots are the engine operating points when the battery is not outputting energy for adjustment. The red point is the adjusted engine operating point.
In Hybrid Drive mode, the engine and wheels are virtually mechanically decoupled in order to operate the engine at the best fuel economy. The required power of the drive motor is compensated by the battery.
In Engine Drive mode, the engine is driven at the same time as the motor. At this time, the generator and the drive motor are involved in adjusting the operating point of the engine to make the engine work at the best fuel economy.
2. Switch modes to improve fuel economy
(1) Switch between EV mode and Hybrid drive mode
Between the EV and Hybrid modes, the iMMD adopts an intermittent hybrid mode, that is, the battery part participates in the power supply. Such a strategy vehicle can increase the speed by up to 50% under low speed/low load conditions; Under high-speed/high-load conditions, the economy has not improved significantly, and the energy efficiency of some working conditions has declined.
(2) Switch between Hybrid drive mode and Engine drive mode
In the Hybrid and Engine hybrid modes, the operating points of the engine and the motor are not completely determined by the operating conditions. Slowly accelerating from cruising speed, engine drive mode is more efficient, up to 12% higher than hybrid mode; hybrid drive mode is more efficient during intense driving.
iMMD system component optimization: engine
The Honda iMMD system uses the Atkinson cycle engine. The characteristics of the Atkinson cycle engine: good economy and poor power. However, the above features are especially suitable for hybrid power, and the shortcomings of power can be compensated by the electric motor.
iMMD Atkinson cycle engine implementation: By designing two cams (VTEC+EVTC), power cam and economic cam (Output Cam/FE Cam), respectively, in start-up conditions and high torque conditions and normal driving In the working condition, the switching of the cam actually realizes the switching between the Otto cycle and the Atkinson cycle (Miller cycle).
Cam profile and principle: The economical cam's intake valve opening time is extended (wide duration). By the intake valve closing, the gas sucked in the intake stroke is discharged again in the compression stroke, resulting in an effect of an Atkinson cycle in which the expansion ratio is greater than the compression ratio.
The effect of the power cam and the economic cam: the economic cam power is significantly reduced, but the economic level is rising.
iMMD system component optimization: motor
1. The design of the first generation iMMD permanent magnet synchronous motor
Means 1: Increase reluctance torque
There are many working points for low load in urban conditions, and it is necessary to reduce the magnet torque to increase the reluctance torque. Because under low torque conditions, the iron loss caused by magnetic flux fluctuations cannot be ignored.
Renovating the position of the magnetic steel, the increased reluctance torque increases the output torque of the entire motor by up to 82%.
Means 2: High voltage
In order to achieve miniaturization of the drive motor and ensure the power of the drive motor, the maximum voltage reaches 700V (the same method is used compared to the third-generation Prius, the maximum drive voltage is 650V)
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