ISG is an abbreviation for Integrated Generator with Starter Function.
The main functions of an ISG hybrid system in a vehicle include idle start-stop, regenerative braking, auxiliary drive, and power generation. The HCU (Hybrid Control Unit) automatically performs these functions by controlling the operating mode of the ISG motor based on the driver's request (accelerator pedal depth), the status of the battery pack's energy storage unit (allowed discharge capacity), the status of the electric drive system (parked, driving), and the overall vehicle status.
The Mercedes-Benz 400 hybrid vehicle is used as an example for illustration. The Mercedes-Benz 400 represents the high-end level of ISG hybrid technology. Its main components are shown in Figure 2-34: an electric power assist system consisting of a high-voltage lithium battery module, an electric motor power module, and an electric motor; a DC/DC voltage conversion system; a HEPS hydraulic electric steering system; a power controller, such as the electric motor controller and the DC/DC converter, using a dual electric cooling circulation pump design; a braking system using an electric vacuum pump, a vacuum booster, and an ABS control unit in conjunction with the electric motor to achieve regenerative braking; and an electronically controlled electric compressor for air conditioning.
Figure 2-34 shows the main components of the ISG hybrid system (Mercedes-Benz electric vehicle).
Its powertrain structure is shown in Figure 2-35, consisting of a six-cylinder engine, an electric motor, a seven-speed automatic transmission, a lithium-ion battery, a power control module, a 12V alternator, and a DC/DC converter.
Figure 2-35 shows the hybrid system structure of the Mercedes-Benz 400.
As shown in Figures 2-36 and 2-37, the crankshaft speed and position signals of the engine use the outer rotor of the electric motor connected to the engine crankshaft as the signal wheel. The stator and rotor of the electric motor adopt the method of inner stator coil and outer rotor permanent magnet. The inner stator coil is supported by the stator bracket. The outer permanent magnet rotor is connected to the crankshaft position/speed signal wheel. The through hole on the inner hub of the signal wheel is connected to the rear end of the engine crankshaft.
Figure 2-36 Structural Assembly Diagram of the Electric Motor in the Mercedes-Benz 400 Hybrid Vehicle
Figure 2-37 Exploded view of the electric motor structure of the Mercedes-Benz 400 hybrid vehicle
High-end cars (such as Mercedes-Benz and BMW) use original hydraulic automatic transmissions. To prevent the clutch oil pressure in the transmission from being too low, an electric ATF oil pump is added to the hydraulic automatic transmission, as shown in Figure 2-38.
Figure 2-38 Mercedes-Benz 400 Hybrid Car 7-speed Automatic Transmission
The hybrid power management system is responsible for coordinating the interactions between the various subsystem components. This management system is integrated into the ECU and communicates with system units such as the automatic transmission, battery, and power electronics via a CAN-bus.
Among them, the power electronics equipment is responsible for managing the energy flow between the electric motor and the high-voltage battery. In addition to the pulse inverter that controls the electric motor, it also includes a DC transformer that can convert the current from the generator or battery into 12V DC power to support the operation of the vehicle's electrical system.
The hybrid power management system can instantly analyze and select the ideal operating strategy based on the battery's state of charge, vehicle speed, and other specific parameters. This operating strategy is a key component of the transmission system control software, connecting various systems to optimize the use of battery power for maximum efficiency, thereby eliminating the drag generated by engine drag. At high-speed stable driving conditions (up to 160 km/h), when the driver releases the accelerator, the V6 engine will completely disengage from the automatic transmission under the control of the clutch, avoiding unnecessary friction loss, increasing vehicle coasting distance, and thus reducing fuel consumption.
Taking the Touareg Hybrid as an example, when the vehicle is below 50 km/h and driven by the electric motor, the V6 engine is not simply shut off completely; the clutch also completely disengages the engine from the 8-speed automatic transmission. Once the driver presses the accelerator pedal at this time, for example, to overtake or accelerate, the turbocharger will immediately and smoothly restart, while simultaneously raising the engine speed to a level suitable for the current vehicle speed.
Furthermore, the energy recovery system can convert the electric motor into a generator during braking, recovering excess energy and storing it in the nickel-metal hydride battery pack. As part of the powertrain system, the automatic start-stop system also helps improve fuel economy in stop-and-go city traffic.
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