Automotive Power Technology Handbook: A Brief Analysis of Three Mainstream Hybrid Technologies

Cars bring us comfort and convenience, but they also cause obvious harm to the environment. How can we solve the contradictions brought about by the existence of cars? Manufacturers have thought of developing new energy models, and using electricity as energy to drive vehicles has become a development trend. However, the road to commercialization of pure electric vehicles is still far away. High costs and unstable batteries constitute the two major bottlenecks that hinder the development of electric vehicles. In order to prevent the stagnation of the research and development of new energy technologies, the hybrid system that uses gasoline engines and electric motors to drive vehicles has become a new topic that manufacturers are competing for attention.

The hybrid models we usually refer to are those that use a gasoline engine and an electric motor as a power source, and the most common one is the Toyota Prius. The gasoline engine used in hybrid models is no different from that of ordinary models, but the one or two electric motors installed have the characteristics of high torque output. The battery pack located at the bottom or rear of the vehicle transmits power to the electric motor to drive the vehicle forward; when the battery power is insufficient, the electric motor can work in generator mode to charge the battery pack. Below we will introduce you to three mainstream hybrid systems.

THERE IS

IMA - integrated motor assist system was developed by Honda Motor Company. Engineers linked the electric motor and generator to the gasoline engine and placed them in front of the gearbox. The electric motor assists the generator to drive the vehicle. This allows the vehicle to have sufficient driving force even when equipped with a smaller, lower displacement engine. Taking the Civic Hybrid as an example, the minimum displacement of the regular model is 1.8 liters, while the hybrid model has a displacement of only 1.3 liters. Due to the direct connection with the engine, the electric motor cannot work when the engine is turned off.

The electric motor of the first generation IMA hybrid system was too low-power, so the vehicle could not run on pure electricity. Currently, the improved electric motor can independently drive the vehicle to maintain speed when the engine is turned off and the vehicle is in cruise mode. When the vehicle brakes, the generator connected to the engine will recover the kinetic energy when the vehicle decelerates and use it to generate electricity. At the same time, the generator also plays the role of the engine starting motor. When waiting at a red light, the engine will automatically shut down, and the generator will be needed to start it again. Of course, to ensure the reliability of the vehicle, there is also a set of conventional starter motors as a backup. The IMA system is currently the simplest hybrid solution with the lowest maintenance cost.

Hybrid Synergy Drive

Toyota has launched the Hybrid Synergy Drive (HSD), which is also composed of an electric motor and an engine, but the placement is different from Honda's IMA system. One of the electric motors is directly connected to the engine, while the other is not. The most critical design of Toyota's system is the compound planetary gearbox. The engine and the electric motor connected to it are combined to form a drive unit, and the other electric motor forms the second drive unit. These two units can be flexibly deployed by the on-board computer to transmit power to the drive wheels through the gearbox.

When accelerating, the first power unit transmits power to the wheels through the gearbox; in pure electric mode, the second power unit replaces the engine and the electric motor to provide power to the wheels alone, at which time the engine and the electric motor connected to it are both turned off. When the vehicle decelerates, the electric motor of the HSD hybrid system will also be transformed into a generator to charge the battery pack, just like the IMA system. The difference between the two systems will only be reflected when the battery pack is fully charged. When the battery pack is fully charged, the power generated by the engine will be transmitted to the electric motor connected to the engine, which will assist the vehicle in deceleration by intervening in the engine speed. Therefore, when you drive a Toyota brand hybrid car, you don’t need to be overly sensitive to the brake pedal. The deceleration provided by the electric motor is basically enough. The original brake system of the vehicle can only come in handy when parking or encountering an emergency. The birth of this system provides the prerequisite for the wire-controlled brake and throttle system controlled by the on-board computer.

Dual-mode或2-mode Hybrid

The third system comes from General Motors, where the Americans have a completely different concept for hybrid power. Although different from the two Japanese manufacturers, GM's dual-mode hybrid system still uses two electric motors. When in low gear, the first electric motor will transfer power to the second electric motor, which will then work with the engine to transfer power to the wheels; when heavily loaded or in high gear, the engine is still running (this is different from the HSD and IMA engines that can shut down or reduce the number of working cylinders).

When the vehicle accelerates, the first electric motor does not transmit power to the wheels, and the second electric motor still charges the battery pack in the engine working mode; when the vehicle speed further increases, the first electric motor begins to transfer electrical energy to the second electric motor, and at the same time the second electric motor stops charging the battery pack and instead drives the vehicle together with the engine.

The above three hybrid systems are all composed of gasoline engine + electric motor, but Volvo Car Corporation took a unique approach and launched the world's first diesel hybrid car, the V60 plug-in, in 2011. The Volvo V60 plug-in uses a small-displacement diesel engine to power the electric motor, while four wheel-side motors are responsible for driving the wheels.

The advantage of this design is that there is no gearbox and no half-axle, which can greatly reduce the weight of the car and simplify the body structure. At present, this model has not yet been officially mass-produced. However, once it is put on the market, it will inevitably usher in a debate about its attributes. Is it a hybrid or a pure electric model? At present, it may be more appropriate to position it as an extended-range electric vehicle.

The advantages of hybrid technology in saving fuel consumption and reducing emissions are obvious, but its disadvantages are also obvious. First of all, since this technology is relatively new, you need to spend more money to pay for this "first-hand experience". Then this new technology needs to face the problem of safety. The battery pack and dense cables in the car are more likely to release high voltage electricity when an accident occurs or is damaged by human beings. I don't think anyone will feel at ease to pay for the car when they know that their car has the function of electric chair (a tool used to execute criminals in the United States). All of the above have become important factors hindering the commercialization and popularization of hybrid vehicles.