It's a hybrid... but what breed exactly?

Dave Garratt of the GEA looks at the salient points of different hybrid electrical systems

Published:  28 March, 2012

THE CONCEPT

Today, there is a bewildering number of different ways of putting power to the wheels. Here we look at a few of them.

Series Hybrid System:

With the series hybrid system, the internal combustion engine drives a generator, which can either charge the batteries or power an electric motor that drives the transmission. Thus, the gasoline engine never directly powers the vehicle. Because the engine drives a generator and the generator feeds the electric motor - which  in turn drives the transmission - all of the components feed each other, therefore the system is said to be in series.  Search for the Hyundai I-oniq to see a practical example.

Parallel Hybrid System:

With the parallel hybrid system, both the engine and the electric motor turn the transmission at the same time and the transmission then turns the wheels. With a parallel hybrid, both the electric motor and the internal combustion engine provide propulsion power.  Therefore, drive comes from 'parallel' sources - the older Honda Insight IMA used this method with the electric motor built into the flywheel.

Series Parallel Hybrid System:

The most common type of dual power vehicle combines both systems in what is called the Series Parallel Hybrid System.  With the Series Parallel Hybrid System, it is possible to drive the wheels using the dual sources of power (electric motors and/or internal combustion engine) and generate electricity while running on the electric motors.  The system runs the car on power from the electric motors only, or by using both the internal combustion engine and the electric motors together, depending on the driving conditions. Since the generator is integrated into the system, the battery can be charged while the car is running. Let's have a look at some of the components in this configuration:

Electric Motors

Special 'synchronous' A/C motors are used in electric cars, which can efficiently produce strong torque at low speeds. They are also compact, lightweight and very efficient, resulting in smoother starting and acceleration. The motors are 3-phase A/C and utilise permanent rotor magnets positioned in the ideal V-figure configuration.  Most require a high voltage supply, 250/300-volt and provide an output of 50 KW power with 400 Nm of torque.  Most modern hybrids propel the vehicle from standstill up to around 30 MPH by using the drive of the electric motor alone.

Battery:

Most batteries are housed in the boot well area and are nickel metal hydride (Ni-MH).  In addition to being light-weight and having a long service life, the high power output Ni-MH battery provides a high power to weight ratio. The battery voltage is normally around 200-volts; however on the very latest Toyota vehicles it's higher at 288-volts.

Generator:

As with the electric motors, most new systems use a synchronous AC generator. The main achievement over recent years has been to increase the maximum rotation speed of hybrid generators, making it possible to produce substantial electrical power while the car is running in the mid-speed range. The typical maximum rotation speed is now around 10,000 RPM.

Power Split Device

The power splitting device distributes the power produced by the internal combustion engine to the drive train and to the generator. To divide the power efficiently it uses a planetary gear consisting of a ring gear, pinion gears, a sun gear and a planetary carrier.

Power Control Unit

The Power Control Unit consists of an inverter, a voltage-boosting converter and an AC/DC converter to run the car on electric motors.

The inverter converts DC supplied by the battery or voltage-boosting converter to AC in order to turn the electric motors.  It also converts AC generated by the generator into DC to recharge the battery.

As well as acting as a normal engine management ECU, the hybrid system's control unit is responsible for controlling the power distribution between the electric motor and engine for switching between the electric drive and regenerative braking functions.

There are a few simple rules for working on vehicles with an electric motor. These all come down to getting somebody who knows what they are doing to make the big orange cable safe. Always remember:

There are people with certain health conditions that are advised for safety reasons not to work on high-voltage vehicles. In general terms, it's those people fitted with specific electric life-sustaining devices.

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