How Hybrids Work
Hybrid electric vehicles (HEVs) combine the benefits of gasoline engines and electric motors. They can be designed to meet different goals, such as better fuel economy or more power.
Most hybrids use several advanced technologies:
Regenerative Braking. Regenerative braking recaptures energy normally lost during coasting or braking. It uses the forward motion of the wheels to turn the motor. This generates electricity and helps slow the vehicle.
Electric Motor Drive/Assist. The electric motor provides power to assist the engine in accelerating, passing, or hill climbing. This allows a smaller, more-efficient engine to be used. In some hybrids, the electric motor alone propels the vehicle at low speeds, where gasoline engines are least efficient.
Automatic Start/Stop. Automatically shuts off the engine when the vehicle comes to a stop and restarts it when the accelerator is pressed. This reduces wasted energy from idling.
HYBRID SYNERGY DRIVE (TOYOTA)
Toyota’s take on the hybrid drive has a pair of motor-generators, one in-line like the Honda IMA design, one not. The key to its success is the compound planetary gearset in the transmission. In the Toyota system, the petrol engine and one motor-generator are connected to one of the inputs, the second motor-generator to the second input and the wheels to the third. Through a clever use of electronics, the planetary gearbox can be locked and unlocked in various configurations depending on what is required. For example under modest acceleration, the petrol engine drives the planetary gearbox as well as the first motor-generator. The output from that is fed to the second motor-generator along with the output from the gearbox to drive the wheels. In pure electric mode, the first motor-generator freewheels, the petrol engine is turned off and all the electric power is fed to the second motor-generator. Under regenerative braking, the second motor-generator becomes the generator as it does in the IMA system above. The difference is that if the battery pack is full, the energy derived from the second motor-generator is redirected to the first motor-generator which in turn uses it to induce drag in the petrol engine to slow the vehicle down. As a result, the actual brakes in a Toyota Hybrid car do not wear very quickly at all because most of the braking is provided by the motor-generators. Only in severe cases do the brake pads actually engage the brake rotors. This is all made possible by the central engine computer and throttle-by-wire / brake-by-wire system.
DUAL-MODE OR 2-MODE HYBRID (GM)
The third hybrid system comes from GM and has two operating modes as opposed to the single mode of IMA or HSD. It again uses two motor-generators. In first and second gears, the first motor-generator sends power to the second motor-generator, and that coupled with the petrol engine provide the power to the wheels. In higher gears or under heavier loads, the petrol engine always runs (as opposed to the IMA and HSD systems where it can be turned off or have cylinders deactivated). The difference is how the motor-generators work in cooperation with it. As speed increases, the first motor-generator gets to the point where it’s providing no useable input to the drivetrain. At this point, it begins to freewheel and the second motor-generator begins to act as a generator. As speed increases further, the first motor-generator begins to act as a generator again and at this point, its power is once again fed to the second motor-generator which now becomes a motor. Coupled with variable intake timing, direct common-rail injection and a host of other technologies, these all come together to give GM’s take on hybrid technology.