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There are different types of hybrids that should be considered for your needs. For instance, if you are going to primarily use the vehicle for city driving, there are hybrid systems that maximize your city mileage and benefits. If you need a work truck or will be using the vehicle on the highway, there is a different type of hybrid system available. The purpose of this section is to help you understand the differences so that you can select the right hybrid vehicle for you. Types of Drivetrains There are three common types of hybrid drivetrains which include:
The Series Drivetrain The series drivetrain has the electric motor connected directly to the wheels or through a differential. It may or may not have a regenerative system (regen) for braking assistance and to recover the energy from braking. This system has a generator, usually an Internal Combustion Engine (ICE), connected to a generator. The generator charges a battery, or energy storage system such as a flywheel or capacitors, which supply an inverter which varies the voltage and frequency to the electric motor.
The advantages of this type of system include:
The Parallel Drivetrain The parallel drivetrain has an electric motor and ICE operating in parallel with the possibility of the motor also being able to drive a generator to recharge the batteries. The motor and generator may be one unit. Both systems operate through a transmission to the differential.
The advantages of this type of system include:
The Compound Drivetrain The compound drivetrain, also referred to as the power split hybrid, has features of both the series and parallel systems. A standard ICE provides relatively low torque at very low speeds requiring larger ICE sizes for heavier loads, whereas the electric motor provides significant torque across its speed range. In a compound drivetrain, the electric motor(s) can be used to assist the ICE to provide better acceleration performance at lower speeds, or even operate purely electric, with the electric motor then providing support at specific speed ranges in order to optimize efficiency.
The advantages of this type of system include:
Degree of Hybridization No two hybrid designs are exactly alike. Hybrids can be further broken down into degrees of hybridization, including:
Full or Strong Hybrid A strong hybrid utilizes just the ICE, battery power or both in combination. For vehicles that primarily operate with the electric motor, a larger, high capacity battery is required. A strong hybrid is normally provided a compound powertrain and requires significant coordination and control of both the ICE and motor drives. Strong hybrids also utilize regen to recover braking power for recharging the batteries while the vehicle is coasting or braking, and the battery is recharged by the engine. Most of these systems shut down the engine while at a stop to conserve fuel and use the electric motor to restart the engine when called upon. Common strong hybrid types include:
Power Assist or Mild Hybrid The mild hybrid uses the ICE for primary power with a torque boosting electric motor connected to a relatively conventional powertrain. The motor is either mounted in between the engine and transmission or a belted system that acts as a starter while providing a boost during acceleration. The different configurations of mild hybrids depend upon the starting and stopping of the ICE while the vehicle is idling or as it comes to a stop. Plug-In Hybrid-Electric The Plug-In Hybrid is, in effect, a series hybrid system by definition. Similar to a pure electric plug-in vehicle, the plug-in hybrid uses an on-board generator to provide charging to the batteries in order to boost distance and give the operator the option of using household voltage to charge the vehicle overnight for short distances (an average of 40 miles) then use the generator to extend the range or to use just the on-board generator. It should be noted that a parallel plug-in system is not a plug-in hybrid-electric, but is actually only a parallel hybrid with the ability to recharge the batteries by plugging it in. The true definition requires that the ICE, or other energy source, not come into direct contact with the powertrain. Plug-In Electric The pure electric vehicle has a much larger, higher capacity battery that is charged from a source outside the vehicle. These will often have a relatively short range and require an average of 6 to 8 hours to charge. Some longer range vehicles exist, such as GM’s original EV1 (out of circulation) and the Tesla with ranges over 100 miles on a single charge.
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