Analysis of Honda IMMD's latest fourth-generation hybrid system

1. Introduction of assembly parameters

Honda's hybrid system IMMD has gone through four generations of technology iterations so far, and the fourth generation technology has made great improvements. The overall configuration has changed from a coaxial arrangement to a parallel axis arrangement, the engine system has been optimized from PFI port injection to direct injection, the motor torque and speed have been further improved, and the generator speed and power have been further improved. The fourth generation IMMD hybrid system technology upgrades are summarized in the following aspects.

The latest fourth-generation development purpose: to improve power and efficiency.

Power unit composition: 2.0L direct injection engine, the engine is upgraded from PFI to GDI;

FDU (hybrid mechanism): The generator, motor and reducer are integrated, the FDU speed is increased by 12%, and the FDU torque is increased by 6% (the generator diameter is reduced, the coaxial axis is changed to parallel axis, and the axial direction is shorter);

PCU (Power Control Unit): high voltage controller module;

IPU (Intelligent Power Unit): battery control unit;

The engine can achieve high and low gear drive (increasing the engine low speed and high load, replacing the previous drive motor operation) - to meet the use of heavier vehicles;

The vehicle weight is allowed to increase by 10%, and the maximum speed increases by 12% (the system efficiency in this working condition increases by 3%);

Honda's latest vehicle layout includes HEV and PHEV, expanding global applications, fully covering vehicle weight, achieving high vehicle speed, and meeting the market's requirements for high driving force.

The vehicle assembly developed in the early stage is compared with the latest generation of vehicles and assemblies. The detailed vehicle and powertrain parameters are shown in Table 1 below.

The latest generation of Honda IMMD is the fourth generation hybrid upgrade. The drive motor and generator of the previous three generations of hybrid systems are coaxially arranged. The main arrangement is that the generator, motor, and reduction transmission are coaxially arranged in sequence. The main disadvantage is that the axial size is large and the shaft system is long, which is not conducive to processing and manufacturing and space optimization. The specific coaxial structure is shown in Figure 2-1.

The fourth-generation IMMD hybrid configuration has undergone significant changes and optimizations compared to previous generations. The main optimizations include the following aspects:

1. Two-speed parallel shaft arrangement FDU;

2. The engine output is divided into two levels: high and low;

3. The generator and drive motor are arranged in parallel.

The fourth-generation Honda hybrid mechanism is shown in Figure 2-2.

The engine in the new fourth-generation Honda hybrid system has also been greatly improved, changing from port injection to direct injection, with overall improvement in power and torque, and a wider fuel economy range for the engine, which is more conducive to improving economy. The new high-efficiency engine combustion system has been redesigned and optimized, exhaust cooling has been further enhanced, high-pressure injection in the cylinder, and multiple injection strategies have been adopted, which are more conducive to improving economy and emissions. The main optimization and improvement of engine technology are summarized in the following aspects.

1. The compression turbulence energy at top dead center is increased by 14.8% (the piston top shape and air channel are re-optimized);

2. The water jacket is optimized, the cooling area on the exhaust side is increased, the exhaust temperature is reduced, and the equivalent air-fuel ratio area is improved;

3. Port injection is upgraded to direct injection (multiple injection);

The engine power is increased from 107kW to 108.2kW, the engine torque is increased from 175Nm to 187Nm, and the lowest fuel consumption rate in the fuel consumption map is 207g/kWh, as shown in Figure 3-1. The lowest fuel consumption point of the fourth-generation IMMD matching engine is close to that of the third generation. The most important fuel consumption optimization is the expansion of the low fuel consumption area, especially in the direction of engine load, the low fuel consumption area is wider.

The maximum torque of Honda's fourth-generation hybrid system drive motor has been further improved from the original 315Nm to 335Nm, and the maximum speed for maximum sustained power has been increased from the original 13000rpm to 145000rpm.

The maximum torque is increased, the acceleration target of 0.4g is achieved at the start, the maximum speed is increased, and the maximum power continuous area is increased. The drive motor performance curve is shown in Figure 4-1.

Honda's latest generation of hybrid powertrains has undergone major changes to the generator, which has been optimized from being coaxial with the drive motor to being arranged in parallel with the drive motor. In order to achieve a more compact structure, the generator's volume and space have been further optimized.

The maximum torque of the generator is reduced from 85mm to 68mm, meeting the requirement of smaller diameter for smaller space of parallel shafts; the maximum speed is increased from 13,000rpm to 19,000rpm, and the transmission ratio between the generator and the engine is optimized, from 0.51 to 0.33;

The maximum power is further increased from the original 106kW to a maximum power of 120kW, as shown in Figure 5-1.

1. PCU

The new generation PCU structure is shown in Figure 6-1.

PCU includes the integration of motor controller MCU, boost mechanism, DCDC and other major high-voltage devices.

Optimization and improvement in two aspects: miniaturization and power improvement.

The PCU volume has been improved from the original 11.5L to 9.99L. The original PCU power was 34.8kVA, and the latest generation power has achieved 47.3kVA/L.

2. IPU

IPU is a lithium-ion battery control module, and the battery management system is optimized to achieve the expansion of battery capacity and the reduction of battery cell capacity. While the performance is further improved, the volume and weight are further optimized and reduced.

The battery management system is optimized to achieve a 19% capacity expansion, and the battery cell capacity can be reduced by 19% (to achieve the same performance). At the same time, the weight is reduced by 12% and the volume is reduced by 24%.

Honda HEV batteries use an air-cooled structure, and the cooling fan layout is optimized and arranged inside (usually arranged outside), as shown in Figure 6-2 and Figure 6-3.

1. Drive Mode

The new generation Honda hybrid system has similar driving modes compared to the previous generation. The main difference is that the new generation engine drive is divided into two gears, high and low. The main driving modes are still EV, hybrid and engine direct drive, as described below.

EV mode: low speed and low load operation, generally for urban commuting;

Hybrid mode: series and parallel modes to adjust the engine to operate efficiently;

Engine direct drive mode: The engine is divided into two gears, high gear and low gear. The high gear is adjusted to achieve the highest efficiency at high speeds; the low gear is adjusted to expand the high efficiency range. See Figure 7-1.

2. Engine mode improves efficiency

In the engine usage mode, try to use the engine's highest efficiency area. The main basis for improving engine efficiency is as follows.

2.1 The use of the engine suppresses electrical loss;

2.2 The control basis is to track the engine's optimal efficiency point;

2.3 Battery and engine use control for maximum system efficiency.

The output of the engine is perfectly coupled to the battery, as shown in Figure 7-2.

While the engine is running efficiently, the powertrain efficiency also needs to be maximized. The powertrain efficiency mainly includes engine thermal efficiency and electrical loss. The various efficiencies are superimposed to obtain the optimized system efficiency, as shown in Figure 7-3.