Hybrid electric vehicle
Hybrid electric vehicles have three layout forms: series, parallel, and hybrid.
1. Series refers to the engine driving a generator to produce electricity, which is directly delivered to the motor through the motor controller, and the motor generates electromagnetic torque to drive the vehicle. Performance characteristics include:
(1) The engine's operating state is not affected by the vehicle's driving conditions, always operating stably within its optimal working range, thus the engine has good economy and low emissions.
(2) Because there is a battery to 'peak shave' the driving power, the engine's power only needs to meet the power required for the vehicle to operate stably at a certain speed, allowing for the selection of a smaller engine.
(3) There is no mechanical connection between the engine and the drive axle, so there are no requirements for the engine's speed, allowing for a wider range of engine selection, such as high-efficiency gas turbines.
(4) There is no mechanical connection between the engine and the motor, providing greater freedom in the structural layout of the vehicle.
(5) The engine's output must be fully converted into electrical energy before being transformed into mechanical energy to drive the vehicle, requiring a generator and motor with sufficiently large power.
(6) To achieve a good balance of generator output power and avoid overcharging or over-discharging the battery, a larger battery capacity is needed.
(7) The generator converts mechanical energy into electrical energy, the motor converts electrical energy into mechanical energy, and there are energy losses during the charging and discharging of the battery, resulting in a relatively low energy utilization rate from the engine.
2. Parallel refers to the engine being connected to the drive axle through a mechanical transmission device, and the motor is also connected to the drive axle through a power composite device. The vehicle can be driven jointly by the engine and motor or separately by each, with performance characteristics including:
(1) The engine directly drives the vehicle through a mechanical transmission mechanism, with no energy conversion loss, thus the energy utilization rate of the engine's output is relatively high. When the vehicle's driving conditions allow the engine to operate within its optimal range, the fuel economy of parallel HEVs is higher than that of series HEVs.
(2) The motor provides a 'peak shaving' function, allowing the engine's power to be appropriately reduced.
(3) When the motor is only used as an auxiliary drive system, its power can be relatively small.
(4) If equipped with a generator, the generator's power can also be smaller.
(5) With the generator supplementing electrical energy, a smaller battery capacity can meet usage requirements.
(6) Since the engine's operating conditions in a parallel drive system are affected by the vehicle's driving conditions, when the driving conditions vary greatly, the engine will often operate under less favorable conditions. Therefore, the engine's emissions are higher than those of series systems.
(7) Due to the direct mechanical connection between the engine and the drive axle, a transmission device is needed to adapt to changes in the vehicle's driving conditions. Additionally, since the engine and motor are driven in parallel, a power composite device is also required, making the transmission mechanism of the parallel drive system relatively complex.
3. The hybrid drive system is a combination of series and parallel, where part of the power generated by the engine is transmitted to the drive axle through mechanical transmission, while another part drives the generator to produce electricity. The structural form and control method of the hybrid drive system fully leverage the advantages of both series and parallel systems, allowing for more optimized matching of components such as the engine, generator, and motor, thereby ensuring that the system operates in an optimal state under more complex conditions, making it easier to achieve emission and fuel consumption control targets.
Disadvantages: The system structure is relatively complex; fuel-saving effects during long-distance high-speed driving are not obvious.